Transition Metal Precursor and Cathode Active Material Prepared from the Same

Abstract

The present invention provides a transition metal precursor having a particle structure in the form of secondary particles formed by the aggregation of primary particles, wherein when a central part and a surface part are distinguished based on the center of the particle, the central part essentially includes pore-inducing particles that form pores during calcination, and the surface part optionally includes pore-inducing particles, and an anode active material having buffer pores prepared therefrom.

Description

Technology Field

[0001] The present invention relates to a transition metal precursor and an anode active material prepared therefrom, and more specifically, to a transition metal precursor having a particle structure in the form of a secondary particle, wherein a void-inducing particle that forms a void upon calcination is contained in the center, and to an anode active material prepared from said precursor by calcination and containing a buffer void. Background Technology

[0002] Due to characteristics such as high energy density and long lifespan, secondary batteries are utilized as a major energy source in various fields, including small devices like mobile phones and laptops as well as medium and large-sized devices such as electric vehicles and energy storage systems. Consequently, high-energy-density Ni-based active materials, such as NCM and NCA, are gaining attention as cathode active materials for next-generation lithium secondary batteries.

[0003] When these secondary batteries are charged and discharged, volume contraction or expansion of the active material occurs, and during this process, microcracks may form in the active material particles.

[0004] In regions where microcracks have occurred within the active material particles, additional side reactions may take place, and there is a possibility that the cracks may deepen or the active material particles may fracture due to byproducts of these side reactions that increase with charging and discharging.

[0005] Microcracks and breakdown of active material particles not only cause additional side reactions with the electrolyte but also act as a major cause of battery performance degradation and reduced lifespan stability.

[0006] In this regard, many coating techniques are being attempted to suppress reactions on the surface of active materials and reduce the breakdown of active material particles; however, there are cases where the coating layer collapses as the battery cycle increases due to the volume contraction / expansion of active material particles during the charging and discharging process.

[0007] Therefore, there is a high need in the industry for technology capable of solving the problems of reduced lifespan characteristics and particle strength caused by volume changes due to repeated charging and discharging. The problem to be solved

[0008] The present invention aims to solve the problems of the prior art described above and technical challenges that have been requested over time.

[0009] After conducting in-depth research and various experiments, the inventors of the present application developed a novel transition metal precursor having a particle structure in the form of secondary particles and containing pore-inducing particles at a predetermined location. During the calcination process for manufacturing an active material, the pore-inducing particles in the precursor melt or decompose to form buffer pores. The inventors confirmed that the cathode active material manufactured in this way exhibits electrochemical properties such as high particle strength and excellent lifespan characteristics due to the action of the buffer pores, and thus completed the present invention. means of solving the problem

[0010] Accordingly, the transition metal precursor according to the present invention has a particle structure in the form of secondary particles in which primary particles are aggregated, and when the central part and the surface part are distinguished based on the center of the particle, the central part essentially includes pore-inducing particles that form pores during calcination, and the surface part optionally includes pore-inducing particles.

[0011] In other words, the present invention provides a technology capable of improving lifespan stability by controlling the shape of the transition metal precursor, and ultimately the shape of the cathode active material, thereby reducing the degree of volume contraction / expansion during charging and discharging. In particular, while typically, as the Ni content increases, fewer pores are formed and lifespan characteristics deteriorate, lifespan characteristics can be improved by artificially forming pores (buffer pores) at specific locations within the particles. Furthermore, it leads to an improvement in particle strength by preventing particle disintegration through the suppression of microcrack formation.

[0013] Since the above-mentioned pore-inducing particles function to form pores at desired locations within the active material after calcination, the type thereof is not particularly limited as long as it is a material capable of forming pores during the calcination process for manufacturing the cathode active material while maintaining its shape within the transition metal precursor.

[0014] In one specific example, the pore-inducing material may be a material that is insoluble to sparingly soluble in water and melts and / or decomposes upon calcination to form pores. Generally, since transition metal precursors containing two or more types of transition metals are prepared through co-precipitation in a basic solution, it is desirable that the pore-inducing material, which requires precursor nucleation and shape retention, be insoluble in water and basic solutions, and at least sparingly soluble. Additionally, it may be necessary to remove it through a melting and / or decomposition process caused by high heat during a high-temperature calcination process.

[0015] There may be various materials that satisfy this, for example, polymer resins containing carbon and hydrogen as main components may be used, and if such polymer resins can melt or decompose at the firing temperature, thermoplastic resins and thermosetting resins are not particularly distinguished, and examples of the above thermoplastic resins include polyethylene, polypropylene, polystyrene, polyvinyl chloride, etc., but are not limited to these.

[0017] The size of the above-mentioned void-inducing particles can be set regardless of the particle shape.

[0018] When the pore-inducing particles are spherical or have a similar shape, for example, the ratio (d1 / D1) of the average diameter (d1) of the pore-inducing particles and the average diameter (D1) of the precursor particles may be in the range of 0.1 to 0.4.

[0019] The size of these particles can be calculated directly from cross-sectional images via FIB or mechanically calculated using FE-SEM.

[0020] Generally, it is known that as the pore size increases, the reaction surface area of ​​the active material particles widens, leading to increased contact with the electrolyte and side reactions, which in turn reduces the lifespan and lowers the particle strength. However, according to the present invention, the lifespan characteristics and particle strength of the active material particles can actually be improved by the method of 'artificial pore formation.' This is because the buffer pores inside the active material particles act as a buffer volume when the volume of the active material contracts or expands during the charging and discharging process of the battery, thereby suppressing the occurrence of cracks or collapse of the active material particles. The results related to this can be confirmed in the experimental details described later.

[0021] In the above setting range, if d1 / D1 < 0.1, the voids formed in the active material particles are too small to obtain an effective buffering effect, and if d1 / D1 > 0.4, the decrease in particle strength due to empty spaces within the particles may be dominant over the improvement in particle strength due to the suppression of microcracks, so it is undesirable.

[0023] In cases where it is difficult to assume that the pore-inducing particles have a spherical or similar shape, for example, the cross-sectional area of ​​the pore-inducing particles may be in the range of 1 to 16% based on the average cross-sectional area of ​​the precursor particles.

[0024] The reason for setting the upper and lower limits of the above range can be interpreted as the same as that in d1 / D1 explained earlier.

[0026] As previously explained, the center and the surface layer of the transition metal precursor of the present invention are distinguished according to the inclusion conditions of the pore-inducing particles. In one specific example, the center is defined as a region where the distance from the center of the particle is 0.5R based on the average distance (R) from the center of the precursor particle to the surface of the particle, and can be set to satisfy the condition that at least 80% of the cross-sectional area of ​​the pore-inducing particles is located in the center based on the cross-section of the precursor particle.

[0027] As defined above, a form in which pore-inducing particles are mainly located in the center can be defined as a 'centralized distribution,' which is a concept contrasted with a 'dispersed distribution' in which a single pore-inducing particle is located away from the center or two or more pore-inducing particles are scattered throughout the interior of the precursor. In other words, it is confirmed that it is undesirable for a form in which only one pore-inducing particle exists within the precursor particle and is biased away from the center of the particle, or in which two or more pore-inducing particles exist within the precursor particle and are scattered throughout rather than clustered mainly in the center. Furthermore, if the pore-inducing particles have a scattered distribution, the interface between the pores formed in the active material and the secondary particles becomes closer, which can lead to an extreme decrease in particle strength in that region. Therefore, it is desirable to have a centralized distribution, and to achieve this, it may be necessary to satisfy the above-mentioned setting condition (at least 80% existing in the center of 0.5R).

[0029] In one specific example, the surface layer is defined as the region from the outer side of the center to the particle surface, and may be a structure comprising a radial crystal phase in which the primary particle is oriented from the center of the secondary particle to the surface.

[0030] When transition metal compound (precursor) particles are aggregated (nucleated) and grown on pore-inducing particles, a structure ('columnar structure') containing radial crystal phases of primary particles can be formed. This columnar structure is desirable because it significantly reduces the volume shrinkage / expansion of the active material, thereby further improving particle strength and lifespan stability.

[0032] The transition metal precursor of the present invention is particularly preferred for a precursor containing 80 mol% or more of Ni based on the total transition metal content.

[0033] The formation of pores (buffer pores) within the active material due to pore-inducing particles inside the precursor implies a decrease in the overall density of the active material, which leads to a reduction in capacity. However, since the capacity of the active material increases with higher Ni content, the phenomenon of capacity reduction caused by the aforementioned pore formation can be largely offset. Furthermore, as the porosity of the active material after calcination generally decreases with higher Ni content, the degradation of lifespan characteristics due to microcracks caused by shrinkage / expansion of the active material is exacerbated; however, despite the high Ni content, lifespan characteristics can be improved through the artificial pore formation according to the present invention.

[0035] The present invention also provides a method for manufacturing the transition metal precursor, wherein the manufacturing method may comprise the following steps.

[0036] (a) A process of preparing an aqueous solution of transition metals containing salts of transition metals and pore-inducing particles;

[0037] (b) A process of forming a precursor seed by adding an aqueous sodium hydroxide solution dropwise while stirring the above transition metal aqueous solution to maintain a predetermined pH level;

[0038] (c) a process of precipitating a transition metal hydroxide by stirring at an increased stirring speed while maintaining or lowering the pH level in the solution in which the precursor seed is formed; and

[0039] (d) A process of filtering, washing, and drying the above transition metal hydroxide.

[0040] The method of adding pore-inducing particles in advance during the preparation stage of the transition metal aqueous solution so that they are included at a predetermined location within the finally prepared transition metal precursor is, in itself, differentiated from the prior art.

[0042] These pore-inducing particles are controlled to be included in a desired location by changing the stirring conditions in process (b) and process (c), that is, by increasing the stirring speed in process (c) compared to the stirring speed in process (b).

[0043] In one specific example, by setting the stirring speed in process (b) to a range of 200 to 600 rpm and the stirring speed in process (c) to a range of 800 to 1200 rpm, the pore-inducing particles can be positioned within the precursor to have a centrally localized distribution rather than a scattered distribution. In the experimental details described below, the effect of changing the stirring speed can be confirmed in the results where a centrally localized distribution was created in Examples 1 to 3, where conditions other than the stirring speed were mutually identical, whereas a scattered distribution was created in Comparative Examples 4 to 6. Similarly, this effect can be confirmed in the results where a centrally localized distribution was created in Examples 4 to 6, where conditions other than the stirring speed were mutually identical, while a scattered distribution was created in Comparative Examples 7 to 9.

[0045] In addition, the pH level in the above processes (b) and (c) can be adjusted as needed.

[0046] In one example, the pH level in process (c) can be set to be the same as the pH level in process (b).

[0047] In another example, the pH level in the above process (c) can be set to decrease sequentially, and by setting the pH level condition in this way, a columnar structure can be formed, which is a structure containing a radial crystal phase in which primary particles are oriented from the center of the secondary particles to the surface, mainly in the surface layer, and this can be confirmed from the results of Examples 4 to 10 in the experimental content described later.

[0048] In one specific example, the pH level in process (b) is set to 11.5 to 11.6, and in process (c), the pH level can be set to sequentially decrease to a total of three levels: 11.0 to 11.2, 10.7 to 10.9, and 10.3 to 10.5.

[0050] The present invention also provides a positive electrode active material having a particle structure in the form of secondary particles formed by the aggregation of primary particles, wherein when a central part and a surface part are distinguished based on the center of the particle, the central part essentially includes a buffering pore, and the surface part optionally includes a buffering pore, and the buffering pore alleviates stress concentration within the particle.

[0051] The pore-inducing particles within the transition metal precursor described above are removed during the calcination process for manufacturing the cathode active material to form buffer pores. These pores act as a buffer volume against externally applied shocks as well as volume expansion / contraction caused by repeated charging and discharging processes, thereby providing electrochemical properties such as high particle strength and excellent lifespan characteristics.

[0053] In one specific example, the buffer pores may be formed by melting and / or thermally decomposing the pore-inducing particles contained in the transition metal precursor as previously described by heat treatment.

[0055] Since the positive electrode active material is prepared by calcining a mixture of the above-mentioned transition metal precursor and lithium raw material in a high temperature and oxidizing atmosphere, the morphological characteristics of the obtained positive electrode active material are largely identical or similar to those of the transition metal precursor. Accordingly, in some specific examples, the positive electrode active material may have the following characteristics based on the transition metal precursor in terms of morphology.

[0056] In the first example, the ratio (d2 / D2) of the average diameter (d2) of the buffer void and the average diameter (D2) of the positive active material particle is in the range of 0.1 to 0.4.

[0057] In the second example, the average cross-sectional area of ​​the buffer void is in the range of 1 to 16% based on the average cross-sectional area of ​​the positive active material particles.

[0058] In the third example, the center is defined as a region where the distance from the center of the particle is 0.5R based on the average distance (R) from the center of the positive active material particle to the particle surface, and at least 80% of the cross-sectional area of ​​the buffer void is located in the center based on the cross-section of the positive active material particle.

[0059] In the fourth example, the surface layer is defined as the region from the outer side of the center to the particle surface, and includes a radial crystal phase in which the primary particle is oriented from the center of the secondary particle to the surface.

[0061] The present invention also provides a secondary battery characterized by including the above positive active material.

[0062] Since the composition and manufacturing method of secondary batteries are known in the art, a detailed description thereof is omitted in this specification. Effects of the invention

[0063] As explained above, the transition metal precursor according to the present invention is based on a novel structure in which pore-inducing particles are included at a predetermined position, and during the calcination process for manufacturing an active material, the pore-inducing particles are melted or decomposed to form buffer pores, and the cathode active material manufactured in this way has the effect of exhibiting electrochemical properties such as high particle strength and excellent lifespan characteristics through the action of the buffer pores. Brief explanation of the drawing

[0064] Figure 1 is a FIB-SEM image of the positive electrode active material of Comparative Example 1; Figure 2 is a FIB-SEM image of the positive electrode active material of Example 5. Specific details for implementing the invention

[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.

[0067] [Comparative Example 1]

[0068] Nickel precursor NiSO4, A transition metal aqueous solution with a concentration of 2.0 M, prepared by mixing a cobalt precursor CoSO4 and a manganese precursor MnSO4 in a molar ratio of 0.89:0.04:0.07, is introduced into a reactor at a rate of 0.3 L / h to prepare the transition metal aqueous solution; subsequently, an aqueous sodium hydroxide solution is added dropwise to the aqueous solution under stirring conditions of 50°C and 1,200 rpm to maintain the pH level at approximately 11.0–11.2, and the reaction mixture is stirred for 5 hours to neutralize the aqueous solution, thereby producing a transition metal hydroxide, Ni 0.89 Co 0.04 Mn 0.07 (OH)2 was precipitated.

[0069] The above transition metal hydroxide was filtered, washed with distilled water, and dried in a 100°C hot air dryer for 10 hours to prepare nickel-cobalt-manganese hydroxide as a positive electrode active material precursor. The above precursor and lithium hydroxide were mixed in a molar ratio of 1:1.03, heated at a heating rate of 5°C, and then calcined at 750°C for 17 hours to obtain a positive electrode active material in the form of secondary particles with a size of 12 μm.

[0071] [Comparative Example 2]

[0072] NiSO4, A positive electrode active material was obtained using the same method as Comparative Example 1, except that the molar ratio of CoSO4 to MnSO4 was 0.60:0.20:0.20.

[0074] [Comparative Example 3]

[0075] Nickel precursor NiSO4, A transition metal aqueous solution with a concentration of 2.0 M, prepared by mixing a cobalt precursor CoSO4 and a manganese precursor MnSO4 in a molar ratio of 0.89:0.04:0.07, is introduced into a reactor at a rate of 0.3 L / h to prepare the transition metal aqueous solution. Subsequently, after the precursor seed is generated under stirring conditions of 50°C and 1,200 rpm, an aqueous sodium hydroxide solution is added dropwise in stages to the aqueous solution so that the pH level changes sequentially in three stages: 11.0–11.2, 10.7–10.9, and 10.3–10.5. The reaction mixture is then stirred for 5 hours to neutralize the aqueous solution, thereby producing the transition metal hydroxide Ni 0.89 Co 0.04 Mn 0.07 (OH)2 was precipitated.

[0076] The above transition metal hydroxide was filtered, washed with distilled water, and dried in a 100°C hot air dryer for 10 hours to produce nickel-cobalt-manganese hydroxide as a positive electrode active material precursor. The above precursor and lithium hydroxide were mixed in a molar ratio of 1:1.03, heated at a heating rate of 5°C, and then calcined at 750°C for 17 hours to obtain a positive electrode active material in the form of secondary particles with a size of 12 μm.

[0078] [Comparative Example 4]

[0079] Nickel precursor NiSO4, A transition metal aqueous solution was prepared by introducing a 2.0 M concentration metal aqueous solution, in which a cobalt precursor CoSO4 and a manganese precursor MnSO4 were mixed in a molar ratio of 0.89:0.04:0.07, and polypropylene particles with an average diameter of 1 μm into a reactor at a rate of 0.3 L / h. Subsequently, an aqueous sodium hydroxide solution was added dropwise to the aqueous solution under stirring conditions of 50°C and 1,200 rpm to maintain the pH level at approximately 11.5–11.6, and the reaction mixture was stirred for 5 hours to neutralize the aqueous solution, thereby producing a transition metal hydroxide, Ni 0.89 Co 0.04 Mn 0.07 (OH)2 was precipitated.

[0080] The above transition metal hydroxide was filtered, washed with distilled water, and dried in a 100°C hot air dryer for 10 hours to produce nickel-cobalt-manganese hydroxide as a positive electrode active material precursor. The above precursor and lithium hydroxide were mixed in a molar ratio of 1:1.03, heated at a heating rate of 5°C, and then calcined at 750°C for 17 hours to obtain a positive electrode active material in the form of secondary particles with a diameter of 12 μm.

[0082] [Comparative Example 5]

[0083] A positive electrode active material was obtained in the same manner as in Comparative Example 4, except that polypropylene particles with an average diameter of 3 μm were used.

[0085] [Comparative Example 6]

[0086] A positive electrode active material was obtained in the same manner as in Comparative Example 4, except that polypropylene particles with an average diameter of 5 μm were used.

[0088] [Example 1]

[0089] Nickel precursor NiSO4, A transition metal aqueous solution was prepared by introducing a 2.0 M concentration metal aqueous solution, in which a cobalt precursor CoSO4 and a manganese precursor MnSO4 were mixed in a molar ratio of 0.89:0.04:0.07, together with polypropylene having an average diameter of 1 μm into a reactor at a rate of 0.3 L / h. Subsequently, a sodium hydroxide aqueous solution was added dropwise to the aqueous solution at 50°C and 400 rpm stirring conditions to maintain the pH level at approximately 11.5–11.6, thereby forming a precursor seed. Afterward, the reaction mixture was stirred for 5 hours at an increased stirring speed of 1000 rpm while maintaining the pH, thereby neutralizing the aqueous solution and the transition metal hydroxide Ni 0.89 Co 0.04 Mn 0.07 (OH)2 was precipitated.

[0090] The above transition metal hydroxide was filtered, washed with distilled water, and dried in a 100°C hot air dryer for 10 hours to produce nickel-cobalt-manganese hydroxide as a positive electrode active material precursor. The above precursor and lithium hydroxide were mixed in a molar ratio of 1:1.03, heated at a heating rate of 5°C, and then calcined at 750°C for 17 hours to obtain a positive electrode active material in the form of secondary particles with a diameter of 12 μm.

[0092] [Example 2]

[0093] A positive electrode active material was obtained in the same manner as in Example 1, except that polypropylene particles with an average diameter of 3 μm were used.

[0095] [Example 3]

[0096] A positive electrode active material was obtained in the same manner as in Example 1, except that polypropylene particles with an average diameter of 5 μm were used.

[0098] [Comparative Example 7]

[0099] Nickel precursor NiSO4, A transition metal aqueous solution was prepared by introducing a 2.0 M concentration metal aqueous solution, in which a cobalt precursor CoSO4 and a manganese precursor MnSO4 were mixed in a molar ratio of 0.89:0.04:0.07, together with polypropylene having an average diameter of 1 μm into a reactor at a rate of 0.3 L / h. Subsequently, a sodium hydroxide aqueous solution was added dropwise to the aqueous solution under stirring conditions of 50°C and 1,200 rpm to maintain the pH level at approximately 11.5–11.6, thereby forming a precursor seed. The reaction mixture was then stirred for 5 hours to sequentially change the pH level in three stages: 11.0–11.2, 10.7–10.9, and 10.3–10.5, thereby neutralizing the aqueous solution and the transition metal hydroxide Ni 0.89 Co 0.04 Mn 0.07 (OH)2 was precipitated.

[0100] The above transition metal hydroxide was filtered, washed with distilled water, and dried in a 100°C hot air dryer for 10 hours to produce nickel-cobalt-manganese hydroxide as a positive electrode active material precursor. The above precursor and lithium hydroxide were mixed in a molar ratio of 1:1.03, heated at a heating rate of 5°C, and then calcined at 750°C for 17 hours to obtain a positive electrode active material in the form of secondary particles with a diameter of 12 μm.

[0102] [Comparative Example 8]

[0103] A positive electrode active material was obtained in the same manner as in Comparative Example 7, except that polypropylene particles with an average diameter of 3 μm were used.

[0105] [Comparative Example 9]

[0106] A positive electrode active material was obtained in the same manner as in Comparative Example 7, except that polypropylene particles with an average diameter of 5 μm were used.

[0108] [Example 4]

[0109] Nickel precursor NiSO4, A transition metal aqueous solution was prepared by introducing a 2.0 M concentration metal aqueous solution, in which a cobalt precursor CoSO4 and a manganese precursor MnSO4 were mixed in a molar ratio of 0.89:0.04:0.07, together with polypropylene having an average diameter of 1 μm into a reactor at a rate of 0.3 L / h. Subsequently, a sodium hydroxide aqueous solution was added dropwise to the aqueous solution under stirring conditions of 50°C and 400 rpm to maintain the pH level at approximately 11.5–11.6, thereby forming a precursor seed. The pH level was then controlled to change in three stages: 11.0–11.2, 10.7–10.9, and 10.3–10.5. The stirring speed was increased to 1000 rpm, and the reaction mixture was stirred for 5 hours to neutralize the aqueous solution, thereby producing the transition metal hydroxide Ni 0.89 Co 0.04 Mn 0.07 (OH)2 was precipitated.

[0110] The above transition metal hydroxide was filtered, washed with distilled water, and dried in a 100°C hot air dryer for 10 hours to produce nickel-cobalt-manganese hydroxide as a positive electrode active material precursor. The above precursor and lithium hydroxide were mixed in a molar ratio of 1:1.03, heated at a heating rate of 5°C, and then calcined at 750°C for 17 hours to obtain a positive electrode active material in the form of secondary particles with a diameter of 12 μm.

[0112] [Example 5]

[0113] A positive electrode active material was obtained in the same manner as in Example 4, except that polypropylene particles with an average diameter of 3 μm were used.

[0115] [Example 6]

[0116] A positive electrode active material was obtained in the same manner as in Example 4, except that polypropylene particles with an average diameter of 5 μm were used.

[0118] [Example 7]

[0119] NiSO4, A positive electrode active material was obtained in the same manner as in Example 2, except that the molar ratio of CoSO4 to MnSO4 was 0.93: 0.03: 0.04.

[0121] [Example 8]

[0122] NiSO4, A positive electrode active material was obtained in the same manner as in Example 2, except that the molar ratio of CoSO4 to MnSO4 was 0.96: 0.02: 0.02.

[0124] [Example 9]

[0125] NiSO4, A positive electrode active material was obtained in the same manner as in Example 2, except that the molar ratio of CoSO4 to MnSO4 was 0.70: 0.15: 0.15.

[0127] [Example 10]

[0128] NiSO4, A positive electrode active material was obtained in the same manner as in Example 2, except that the molar ratio of CoSO4 to MnSO4 was 0.60: 0.20: 0.20.

[0130] [Experimental Example 1]

[0131] Figures 1 and 2 disclose images taken with a Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) of the positive electrode active material prepared in Comparative Example 1 and the positive electrode active material prepared in Example 5.

[0132] First, looking at the FIB-SEM image in Fig. 1, it can be seen that the positive electrode active material of Comparative Example 1 does not show pores of a significant size and the primary particles are randomly aggregated.

[0133] On the other hand, looking at the FIB-SEM image in Fig. 2, it can be seen that the positive active material of Example 5 has buffer pores of a predetermined size formed in the center of the particles, and the primary particles, which are mainly aggregated in the surface layer, form a columnar structure including radial crystal phases oriented from the center of the secondary particles toward the surface.

[0135] [Experimental Example 2]

[0136] A positive electrode was fabricated by mixing a conductive agent and a binder with the positive electrode active material prepared in each of the above comparative examples and examples in a ratio of 97.5:1:1.5 (active material:conductive agent:binder), coating the mixture onto an aluminum current collector, and drying it. A secondary battery was fabricated using Li metal as the negative electrode and an electrolyte in which 0.7M concentration of LiPF6 and 0.3M concentration of LiFSi were dissolved in an organic solvent composed of ethylene carbonate / ethylmethyl carbonate (mixed volume ratio of EC / EMC = 3 / 7), vinylene carbonate (VC: 1.5 wt%), propanesulfone (PS: 0.5 wt%), ethylene sulfate (Esa: 1 wt%), and 40.2 wt% of LiBF. Subsequently, electrochemical characteristics and physical properties (1 μm particle volume fraction after pressing) were measured under the following conditions, and the results are shown in Table 1 below.

[0138] <Conditions for Electricity Evaluation>

[0139] - Mode: PNE coin cell system

[0140] - C-rate: Charging 0.5C, Discharging 1C

[0141] - Experiment temperature: 45℃

[0142] - Plate composition: Active material : Conductive material : Binder = 97.5 : 1.0 : 1.5, 15.5 mg / cm² 2

[0143] - Electrolyte: 0.7M LiPF6+ 0.3M LiFSI in EC:EMC=3:7 + VC 1.5% + PS 0.5% + ESA 1% + LiBF40.2%

[0144] - Cell Configuration: MFC Type Full Cell

[0146] <SEM 측정 조건>

[0147] - Model: HITACHI (S-4800)

[0148] - Resolution: 1.0㎚ 15㎸, 1.5㎚ 1㎸

[0149] - Magnification: x10,000

[0150] - Electron gun: Cold-cathode field emission type electron gun

[0151] - Accelerating voltage: 15 kV

[0152] - Detector: SE (BSE)

[0154]

[0155] In Table 1 above, "particles of 1 μm or less (vol%)" represents the proportion of particles of 1 μm or less in the total volume after 5 tons of rolling, and a smaller value indicates a higher particle strength.

[0157] Based on the measurement results of Table 1 above, the following points can be confirmed.

[0159] First, when comparing Comparative Examples 1 to 3, Comparative Examples 1 and 2 are positive active materials that lack both a columnar structure and buffer pores. Comparative Example 1, which has a higher Ni content than Comparative Example 2, has a higher capacity due to the overall lower pore formation, but its lifespan characteristics are relatively inferior. Comparative Example 3, which has a columnar structure, has a relatively higher particle strength compared to Comparative Examples 1 and 2, but its lifespan characteristics are inferior because it lacks buffer pores.

[0161] Second, when comparing Examples 1 to 3 with Comparative Examples 4 to 6, it can be seen that the location of the buffer pores has a direct influence on particle strength and lifespan characteristics. Specifically, in the cathode active materials of Examples 1 to 3, the pores have a distribution that is localized in the center of the particle ('centralized distribution'), thereby exhibiting a buffering effect and improving lifespan characteristics by suppressing particle decay. On the other hand, in the cathode active materials of Comparative Examples 4 to 6, the pores have a distribution that is scattered within the particle ('scattered distribution'), so a significant buffering effect cannot be obtained during the shrinkage / expansion process of the active material due to charging and discharging, and the particle becomes vulnerable to microcracks within the particle, leading to a decrease in particle strength.

[0163] Third, the positive active materials of Examples 4 to 6 and Comparative Examples 7 to 9 differ from Comparative Examples 4 to 6, which do not have a columnar structure, in that they have a columnar structure. Therefore, it can be seen that the positive active materials of Examples 4 to 6 and Comparative Examples 7 to 9 have overall superior particle strength compared to the positive active materials of Comparative Examples 4 to 6.

[0164] Meanwhile, when comparing Examples 4 to 6 with Comparative Examples 7 to 9, it can be seen that under the same conditions, the positive active materials of Examples 4 to 6, which have centrally distributed voids, have relatively superior resistance and lifespan characteristics compared to the positive active materials of Comparative Examples 7 to 9, which have scattered voids.

[0165] Since the pore size is smaller than the optimal size (Example 5: 3 μm) (Example 4: 1 μm), the effect of improving lifespan characteristics is relatively reduced, and conversely, if it is larger (Example 6: 5 μm), the particle strength tends to be relatively low, it can be confirmed that high particle strength and excellent lifespan characteristics can be obtained when the average diameter of the pore-inducing particles and buffer pores falls within the range of 10% to 40% of the average diameter of the secondary particles.

[0167] Fourth, when comparing Examples 7 to 10, it can be seen that the charge / discharge capacity increases in proportion to the Ni content, and the lifespan characteristics are improved by the buffer pores regardless of the Ni content, and in particular, the effect of improving lifespan characteristics by artificial pore formation is prominent in high-Ni active materials with low pore formation.

[0169] 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

Claim 1 A transition metal precursor characterized by having a particle structure in the form of secondary particles formed by the aggregation of primary particles, wherein when a central part and a surface part are distinguished based on the center of the particle, the central part essentially includes pore-inducing particles that form pores during firing, and the surface part optionally includes pore-inducing particles, and the ratio (d1 / D1) of the average diameter (d1) of the pore-inducing particles and the average diameter (D1) of the precursor particles is in the range of 0.1 to 0.

4. Claim 2 A transition metal precursor according to claim 1, characterized in that the pore-inducing particles are a material having the characteristic of being insoluble or sparingly soluble in water and melting or decomposing upon calcination to form pores. Claim 3 delete Claim 4 A transition metal precursor according to claim 1, characterized in that the cross-sectional area of ​​the pore-inducing particles is in the range of 1 to 16% based on the average cross-sectional area of ​​the precursor particles. Claim 5 A transition metal precursor according to claim 1, wherein the center is defined as a region where the distance from the center of the particle is 0.5R based on the average distance (R) from the center of the precursor particle to the surface of the particle, and at least 80% of the cross-sectional area of ​​the pore-inducing particle is located in the center based on the cross-section of the precursor particle. Claim 6 A transition metal precursor according to claim 5, wherein the surface layer is defined as a region from the outer side of the center to the particle surface, and is characterized by including a radial crystal phase in which the primary particle is oriented from the center of the secondary particle to the surface. Claim 7 A transition metal precursor according to claim 1, characterized in that the precursor contains 80 mol% or more of Ni based on the total transition metal content. Claim 8 A method for preparing a transition metal precursor according to claim 1, characterized by comprising the following steps: (a) preparing an aqueous solution of transition metals containing salts of transition metals and pore-inducing particles; (b) forming a precursor seed by adding an aqueous sodium hydroxide solution dropwise while stirring the aqueous solution of transition metals to maintain a predetermined pH level; (c) precipitating a transition metal hydroxide by stirring the solution in which the precursor seed is formed while maintaining or lowering the pH level and increasing the stirring speed; and (d) filtering, washing, and drying the transition metal hydroxide. Claim 9 A manufacturing method according to claim 8, characterized in that the stirring speed in process (b) is set to a range of 200 to 600 rpm, and the stirring speed in process (c) is set to a range of 800 to 1200 rpm. Claim 10 A manufacturing method according to claim 8, characterized in that the pH level in process (c) is set to be the same as the pH level in process (b). Claim 11 A manufacturing method according to claim 8, characterized in that the pH level in the above process (c) is set to decrease sequentially. Claim 12 A manufacturing method according to claim 11, characterized in that the pH level in process (b) is set to 11.5 to 11.6, and the pH level in process (c) is set to sequentially decrease to a total of three levels: 11.0 to 11.2, 10.7 to 10.9, and 10.3 to 10.

5. Claim 13 A positive electrode active material having a particle structure in the form of secondary particles formed by the aggregation of primary particles, wherein when a central part and a surface part are distinguished based on the center of the particle, the central part essentially includes a buffer pore, and the surface part optionally includes a buffer pore, wherein the buffer pore alleviates stress concentration within the particle, and the ratio (d2 / D2) of the average diameter (d2) of the buffer pore and the average diameter (D2) of the positive electrode active material particle is in the range of 0.1 to 0.

4. Claim 14 In claim 13, the positive electrode active material is characterized in that the buffer pores are formed by pore-inducing particles contained in a transition metal precursor being melted and / or thermally decomposed by heat treatment. Claim 15 delete Claim 16 A positive electrode active material according to claim 13, characterized in that the average cross-sectional area of ​​the buffer pore is in the range of 1 to 16% based on the average cross-sectional area of ​​the positive electrode active material particles. Claim 17 A positive electrode active material according to claim 13, wherein the center is defined as a region where the distance from the center of the particle is 0.5R based on the average distance (R) from the center of the positive electrode active material particle to the particle surface, and wherein at least 80% of the cross-sectional area of ​​the buffer void is located in the center based on the cross-section of the positive electrode active material. Claim 18 A positive electrode active material according to claim 17, wherein the surface layer is defined as a region from the outer side of the center to the particle surface, and is characterized by comprising a radial crystal phase in which primary particles are oriented from the center of secondary particles to the surface. Claim 19 In claim 13, the positive active material is characterized by containing 80 mol% or more of Ni based on the total transition metal content. Claim 20 A secondary battery characterized by including a positive electrode active material according to claim 13.

Images