Transition metal precursor for preparation of cathode active material

Abstract

The present invention provides a transition metal precursor for the preparation of a cathode active material, the transition metal precursor comprising an additive element, which is at least one element selected from the group consisting of Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W, wherein when the percentage of a radial distance from the center to the surface of the precursor particle is denoted as L and the content of the additive element in the corresponding distance percentage is denoted as C, a one-to-one function having L as a domain and C as a codomain has a stair gradient in which at least two discontinuous L values (hereinafter, "discontinuous points") exist.

Description

Transition metal precursor for manufacturing positive electrode active material

[0001] The present invention relates to a transition metal precursor for manufacturing an anode active material, and more specifically, to a transition metal precursor having at least two points in which the content of an additive element with respect to the percentage of the radial distance from the center to the surface of the precursor is discontinuous.

[0002] Technologies aimed at improving structural and electrochemical properties by adding dopants to cathode active materials have already been widely presented through various compositions and process conditions. For example, there have been continuous attempts to enhance thermal stability and lifespan characteristics by doping transition metal composite oxides with additional metal elements.

[0003] However, conventional cathode active material doping technology has limitations in that it is difficult to accurately realize the dopant distribution intended during the design phase, as the high-temperature heat treatment of the active material itself during the calcination process makes it prone to dopant diffusion toward the bulk or local concentration variations. Consequently, it is pointed out that the dopant distribution within and between particles becomes non-uniform, and reproducibility is insufficient even when manufactured under identical conditions.

[0004] As a means to mitigate these problems, a so-called pre-doping technique is known, in which dopants are introduced in advance at the precursor stage rather than in the cathode active material. Introducing dopants into the precursor offers the advantages of relatively easy process control and the ability to induce more stable dopant distribution during the particle growth stage, thereby lowering manufacturing difficulty and improving reproducibility.

[0005] Nevertheless, pre-doping of precursors can cause adverse effects, such as dopants blocking lithium diffusion pathways within the crystal lattice or inducing phase changes, and frequently leads to a degradation in the electrochemical performance of cathode active materials produced therefrom.

[0006] Therefore, there is a need in the industry for a new technology that can ensure process difficulty and reproducibility while suppressing the degradation of electrochemical properties through the control of dopant distribution.

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

[0008] After conducting in-depth research and various experiments, the inventors of this application were able to produce a precursor having at least two points in which the function of the content of the additive element relative to the percentage of distance from the center to the surface of the precursor particle is discontinuous. Furthermore, they confirmed that a positive electrode active material produced using such a precursor can suppress the collapse of the layered structure during the insertion and extraction of Li ions during charging and discharging, thereby exhibiting excellent electrochemical properties such as lifespan characteristics, and thus completed the present invention.

[0009] Accordingly, the transition metal precursor of the present invention is a transition metal precursor for manufacturing an anode active material,

[0010] It includes an additive element which is one or more elements selected from the group consisting of Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W;

[0011] When L is the percentage of the radial distance from the center of the precursor particle to the surface, and C is the content of the added element at that distance percentage,

[0012] A one-to-one function with L as the domain and C as the codomain is characterized by including a stair gradient in which there are at least two discontinuous L values ​​(hereinafter referred to as "discontinuity points").

[0013]

[0014] The term 'precursor' used in the present invention refers to a material in the intermediate stage for manufacturing a positive electrode active material, in the form of a complex metal salt such as a transition metal hydroxide, oxyhydroxide, or carbonate, mainly containing a transition metal (Ni, Co, Mn, etc.). The said precursor does not contain lithium, or even if it does, it is in a state where it has not reached the stoichiometric ratio required for manufacturing a positive electrode active material.

[0015] The aforementioned precursor is typically converted into a transition metal oxide-based cathode active material by mixing it with a lithium source, such as lithium hydroxide or lithium carbonate, and then calcining it at high temperatures. During this process, transition metal ions and lithium ions within the precursor combine in stoichiometric ratios to produce the cathode active material. As such, while the precursor is a starting material closely related to the electrochemical properties of the cathode active material, it is a clearly distinct material that is not used as a cathode active material for secondary batteries on its own.

[0016] The transition metal precursor according to the present invention includes an additive element (dopant) that is incorporated within the particle to improve structural stability and, when manufactured into a positive electrode active material, can suppress capacity degradation occurring during repeated charging and discharging. Such additive elements may exist in a specific region within the precursor particle and have unique values ​​depending on the percentage of distance. Furthermore, the effect of the additive element is manifested in the region where it exists, and the effect is generally proportional to the amount of the additive element.

[0017] Although various elements that exhibit an effect of improving the structural stability of precursors or cathode active materials are known, the additive element according to the present invention is preferably one or more selected from Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W. A characteristic of the above elements is that the pH range in which precipitation occurs in the hydroxide state is different from the pH range of precipitation of transition metals. Furthermore, when the precursor to which the above elements are added is manufactured into a cathode active material, the additive element does not participate in the oxidation-reduction reaction, while Ni 2+ It can suppress cation mixing by.

[0018] When the additive element is mixed with an aqueous metal salt solution and co-precipitated as in the conventional method, insoluble fine particles precipitate first due to differences in solubility between transition metal hydroxides, or aggregation does not occur due to the loss of the ion's negative charge neutralization ability under alkaline conditions, resulting in the continuous formation of non-aggregated fine particles (particles of 1 μm or less). To solve this problem, the present invention controls the generation of fine particles by adding the additive element ion after first reacting it with a chelating agent to form a complex, as described below.

[0019] It is preferable that the above-mentioned additive element includes Al. Al having a small ionic radius 3+ Since it can stabilize the primary particle phase structure and improve electrochemical properties even in small amounts, this is due to Al 3+ This is because it suppresses performance degradation caused by the movement of Ni ions within this crystal structure.

[0020]

[0021] As described above, the transition metal precursor according to the present invention includes a stair gradient in which the content (C) of the additive element changes according to a radial distance percentage (L) defined based on the distance from the center of the particle to the surface of the particle. Here, the distance percentage is a value in which the distance percentage from the center of the precursor particle is set to 0 and the distance percentage from the surface of the particle is set to 1, and the larger the value of L, the further it is from the center of the particle and closer to the surface. For example, a location where the distance percentage L is 0.5 corresponds to the midpoint of the distance from the center of the particle to the surface.

[0022] The above distance percentage L is calculated from the radial distance defined based on the shortest length from a specific point on the particle surface to the particle center. In this case, the particle center is defined as the midpoint of the longest line segment connecting the specific point to another point on the particle surface.

[0023] Generally, precursor particles have a three-dimensional quasi-spherical shape. As a result, the direction from the center of the particle to a specific point on the surface may differ. In the present invention, under the premise that the precursor particles have the characteristic of growing in all directions and that a certain degree of sphericity is secured, it is assumed that the content of the additive element at a position corresponding to the same percentage of distance has substantially the same value. Although there may be slight errors during actual measurement due to technical limitations caused by irregularities in particle shape, the closer the precursor particles are to a perfect sphere (the higher the degree of sphericity), the smaller the error in the content of the additive element for the same percentage of distance, and it can be seen that they exhibit substantially the same trend.

[0024]

[0025] The precursor according to the present invention can be modeled by a function C(L) having the distance percentage L as the domain and the content C of the additive element corresponding to the distance percentage L as the codomain. The function C(L) is based on a one-to-one correspondence relationship in which a specific content C of the additive element corresponds to each distance percentage value L (0 ≤ L ≤ 1), and there is no case where two or more different contents of the additive element correspond to the same distance percentage L simultaneously. That is, a single L value must have only one C value, and it is impossible for a single L value to correspond to multiple C values. However, if the sphericity of the precursor is low, an error within a predetermined range may be included in the distance percentage L corresponding to the actual content A of the additive element.

[0026] The precursor according to the present invention comprises a stepwise gradient in which, in the function C(L) defined as above, there exist at least two points of discontinuity where the one-to-one correspondence function, with L as the domain and C as the codomain, is discontinuous and L is a distance percentage value. That is, at some point within the distance percentage region from the particle center to the particle surface, there exists a section where the content of the added element is not continuous and is defined as different values.

[0027] Specifically, the term "discontinuity point" refers, from a mathematical perspective, to a distance percentage value within the domain of the function C(L) such that the left-hand limit of the added element content when approaching from an L value smaller than that distance percentage value and the right-hand limit of the added element content when approaching from an L value larger than that distance percentage value are different. More specifically, it refers to a distance percentage where the content of the added element measured in the direction of the particle center and the direction of the particle surface have different values ​​relative to the said discontinuity point; such a form in which the content of the added element changes stepwise with respect to the said discontinuity point is defined as a stepwise gradient.

[0028]

[0029] In the prior art, the function C(L) generally contains only one discontinuity point. For example, this corresponds to a so-called core-shell pre-doped structure in which the content of the additive element differs inside and outside the particle based on a specific point within the particle. A precursor having such a single discontinuity point has the advantage of making process design and analysis relatively easy by simply dividing the particle center and surface into regions with different additive element content. However, when a single additive element is simultaneously assigned different roles in different regions within the particle, there is a problem in that it is difficult to independently adjust the required content level for each region using only a single discontinuity point. Furthermore, in a structure having only a single discontinuity point, even if the required optimal additive element distribution changes depending on changes in particle size or composition, the regions within the particle can only be divided dichotomously; thus, there are limitations in finely designing and controlling the combination of the width of each region and the content of the additive element.

[0030] Meanwhile, a technique has also been proposed to form a continuous concentration gradient of additive elements within the particle in the radial direction, rather than a stepwise gradient based on discontinuities as in the present invention. It is known that such a continuous gradient structure has the advantage of mitigating stress concentration caused by abrupt compositional changes by theoretically designing the content of additive elements to gradually change from the center of the particle to the surface. However, from the perspective of actual processes, there is a problem in that it is very difficult to repeatedly reproduce a concentration gradient with the same level of slope while various factors are involved simultaneously.

[0031]

[0032] In contrast, the transition metal precursor according to the present invention is characterized by compartmentalizing the internal structure of the particle based on the percentage of distance from the particle center to the particle surface, and designing and controlling the content and distribution of additive elements for each region. That is, it is fundamentally different from the technology of applying a so-called coating or covering, which forms a film by attaching or chemically bonding a novel material to the outer surface of the precursor particle.

[0033] In particular, the transition metal precursor according to the present invention can form a uniform distribution of additive elements while minimizing the generation of fine particles by first reacting the additive element with a chelating agent to produce a complexing agent, rather than simultaneously co-precipitating the metal salt aqueous solution and the additive element by a conventional co-precipitation method during its manufacture, and then mixing and stirring it with the metal salt aqueous solution to improve the solubility of the additive element. In addition, a discontinuous distribution of additive elements can be formed simply by controlling the flow rate of the complexing agent. At this time, it may be desirable to select an optimal chelating agent capable of chelating the additive element.

[0034]

[0035] In one specific example, the transition metal precursor of the present invention can be configured to be partitioned as follows based on the center point and the point of discontinuity closest to the center of the particle among the discontinuities, when the discontinuity closest to the surface of the particle is called the center point and the discontinuity closest to the surface of the particle is called the point point.

[0036] (i) A first region, which is the region from the center of the particle to the center point,

[0037] (ii) a second region, which is the region from the above-mentioned center point to the above-mentioned indicator point, and

[0038] (iii) A third region, which is the region from the above gauge point to the surface of the particle.

[0039]

[0040] The above-described precursor has multiple discontinuity points corresponding to the function C(L), and as previously stated, among these discontinuity points, the discontinuity point closest to the particle center and the discontinuity point closest to the particle surface are defined as the core point and the gauge point, respectively. By defining the core point and gauge point in this way, the precursor particle according to the present invention can be divided into three regions in the radial direction. That is, the distance percentages corresponding to the core point and the gauge point are L, respectively. c and L e If so, the distance percentage is 0 <L c In the first region, L c <L e In the second region, L e <1. It is divided into the third area.

[0041] According to the above definition, the deep point and the gauge point correspond to major boundary points within the precursor particle where the content of added elements changes stepwise in the radial direction, and each region can be understood as a radial functional division region demarcated by these boundary points. For example, the first region is a deep region corresponding to the center of the particle and is involved in lattice stabilization and bulk structure, the second region can contribute to stress relief between the deep and surface layers and the adjustment of ion transport pathways, and the third region is a surface-adjacent region and can perform roles such as interfacial reaction and interfacial resistance control.

[0042] Although the above-mentioned first to third regions are macroscopically divided into three sections, additional discontinuities may exist between them in addition to the center point and the gauge point. In this case, the discontinuity closest to the center of the particle is defined as the center point and the discontinuity closest to the surface of the particle is defined as the gauge point, thereby maintaining the basic structure of the three regions.

[0043]

[0044] In one preferred example, when the average content of the additive element in the first, second, and third regions is denoted as C1, C2, and C3, respectively, C1 to C3 may be set to have different values ​​from each other.

[0045] Here, the criterion for determining the content of added elements in each region is based on the average of the content within that region. Furthermore, "different value" means that the average value of the content of added elements measured in each region has a difference that does not overlap with one another, even when considering the margin of error. By defining it in this way, the first to third regions are clearly distinguished not only in location but also in terms of the composition of added elements.

[0046] As described above, by having C1, C2, and C3 have different values, different functions can be assigned to each region according to the role of the additive element and the required characteristics. For example, the optimal content of the additive element for each region can be set so that the first region is primarily for the purpose of stabilizing the bulk structure and relieving internal stress, the second region is for the purpose of optimizing ion diffusivity, and the third region is for the purpose of controlling interfacial reactions. In this case, the absolute values ​​or relative size relationships of C1, C2, and C3 can be appropriately selected according to the bulk composition and the type and purpose of the additive element.

[0047] Thus, by adopting a stepwise gradient that applies different additive element contents to each of the three regions, it is possible to simultaneously control characteristics that were difficult to satisfy with conventional single discontinuous point structures. Furthermore, compared to conventional continuous concentration gradient structures, the stepwise gradient structure allows for process design based on a finite number of cases, namely C1, C2, and C3; therefore, process control is easier and reproducibility is higher compared to continuous gradient structures, which require the precise reproduction of the same slope profile.

[0048]

[0049] In another preferred example, the average contents of the added elements (C1, C2, C3) in the first, second, and third regions are qualitatively C3-1 <C2의 조건을 만족하도록 설정될 수 있고, 정량적으로 1.5≤C2 / C3≤2.5 및 1.0<C2 / C1≤2.0의 조건을 만족하도록 설정될 수 있다. 실제 함량에서, C1 내지 C3는 하기 조건을 만족하도록 설정될 수 있다.

[0050] (i) 2000 ppm ≤ C3 ≤ C1 ≤ 8000 ppm

[0051] (ii) 4000 ppm ≤ C2 ≤ 10000 ppm

[0052] Step gradients with two discontinuities can also have limitations. For example, the location of the discontinuity and the content of the additive element in each region are strongly correlated, so in certain combinations, the function tends to be skewed toward one side, and there is a problem that it is difficult to simultaneously optimize electrochemical properties and mechanical stability.

[0053] Therefore, C1, C2, and C3 are C3 ◍1 <C2의 조건을 만족하도록 설정될 수 있는 바, 이 경우, 제 2 영역이 세 영역들 중에서 가장 높은 첨가원소 함량을 갖고, 제 1 영역은 제 3 영역과 같거나 그보다 높은 수준의 첨가원소 함량을 갖는다. 더욱 바람직하게는 C3<C1, 즉 표면 인접부의 첨가원소 함량이 가장 적을 수 있다. 특히, 표면 인접부의 첨가원소 함량에 해당하는 C3가 가장 낮은 것이 바람직한데, 이와 같이 본 발명에 따른 전이금속 전구체는 입자 내부의 구조적 안정성을 확보하는 한편, 표면부의 첨가원소 함량이 낮음에도 불구하고 계면 반응을 충분히 제어할 수 있다는 특징을 갖는다.

[0054] In conventional transition metal precursors or cathode active materials, the content of the added element increases monotonically in the radial direction, or at least has a higher content closer to the surface, i.e., C2 <C3의 관계를 갖는 경우가 일반적이다.

[0055] While such a structure allows for the control of interfacial reactivity by concentrating additive elements on the surface, it presented a problem in that it was difficult to sufficiently impart functions such as lattice stabilization, internal stress relief, and ion diffusion pathway control within the particle. Furthermore, C2 with additive elements mainly concentrated on the surface <C3 구조에서는, 입자 내부, 특히 제 2 영역에서의 기능 발현이 부족하다는 문제가 있다. 제 2 영역은 리튬 이온이 반복적으로 출입하는 경로 상에 위치하면서, 내부 응력의 집중이 중첩되는 구간이므로, 이 영역에서 충분한 수준의 첨가원소가 존재해야 한다. 그럼에도 불구하고, 종래 구성에서는 첨가원소가 제 3 영역 쪽으로 과도하게 집중됨으로써, 전구체를 양극 활물질로 제조 시 소망하는 수준의 성능 향상이 발현되지 않는다는 한계가 있었다. 특히, 고니켈(high-Ni)계와 같이 구조 불안정성이 높은 조성의 전구체 및 그로부터 제조된 양극 활물질에서는 표면부가 강화되었음에 반해 반복되는 충방전에 대한 내부 구조 붕괴 및 사이클 특성 저하가 발생하기 쉽다.

[0056] In contrast, the present invention establishes the relationship of the additive element content in the first to third regions as described above, thereby positioning the region with the highest additive element content as the second region. That is, the second region, which is involved in ion diffusion pathways and internal stress relief, is designed as a high-concentration additive element region, so that the intermediate layer located between the interior and the surface of the particle simultaneously performs the roles of structural buffering and diffusion pathway control. More preferably, C3 <C1를 만족하는 것이 유리할 수 있다.

[0057] In order to implement a precursor having the highest content distribution of the additive element C2 among C1 to C3 as described above in the positive electrode active material, it is further desirable to implement such a distribution at the precursor stage.

[0058] Generally, to add additive elements to a positive electrode active material, a transition metal precursor, an additive element source material, and a lithium source material are physically mixed and then subjected to heat treatment; in this case, the additive element diffuses from the surface of the transition metal precursor into the interior of the particle due to heat. Therefore, the additive element inevitably has a higher content outside the particle, and it is practically impossible to accurately distribute the additive element to a desired location within the positive electrode active material through this principle of diffusion. In particular, as in the present invention, C3, which has a higher content of additive element inside the particle <C2 관계를 구현하기 위해서는 극도의 고온을 필요로 하는 바, 해당 소성 조건이 양극 활물질에 미치는 영향을 예측할 수 없으므로 바람직하지 않다. 상기와 같은 이유들로 인해, 입자 내부의 첨가원소 함량이 더 높은 양극 활물질의 제조를 위해서는 전구체 단계에서 첨가원소의 분포를 선제적으로 제어하는 것이 필수적이다.

[0059] Meanwhile, the above configuration, in which the content of additive elements inside the particle is higher than that on the surface, also differs from conventional core-shell structures. The shell structure formed on the outer side of the particle is configured to protect the core from external factors and has a composition and / or physical properties different from the core; generally, specific elements that exert this effect have a higher content outside the particle. That is, regarding additive elements other than those constituting the core, regardless of whether their content is discontinuous or continuous, the content outside the particle is usually higher. Therefore, the precursor according to the present invention, in which the content of additive elements inside the particle is higher, has an essential difference from conventional core-shell structures.

[0060] In quantitative comparison, these contents are 1.5≤C2 / C3≤2.5 and 1.0 <C2 / C1≤2.0의 조건을 만족하도록 설정될 수 있는데, 상기 수치 관계는 영역 간 첨가원소 함량 분포의 구체적인 비율을 한정하는 바, 각 영역이 담당하는 기능이 충분히 분리 및 발현될 수 있도록 상기 수준의 분포 차이를 가진다.

[0061] Specifically, the average content ratio C2 / C3 of the second and third regions is 1.5 to 2.5. If the content ratio is excessively low, the two regions remain within a substantially similar compositional range, making it difficult for the unique function of the second region to be fully exhibited. Furthermore, if C2 / C3 is lower than 1.5, it approaches the high-concentration surface structure generally adopted in the prior art, which is contrary to the design concept aimed at by the present invention.

[0062] The average content ratio C2 / C1 of the second region and the first region is greater than 1.0 and less than or equal to 2.0, so it is desirable that the second region must have a higher content of the added element than the first region, but not exceed twice. In other words, a sufficient difference in content is required between the second region and the first region.

[0063] Meanwhile, although the third region has a lower content than the second region, it is directly involved in interfacial properties, so it is desirable to satisfy the above numerical range (2000 ppm ≤ C3 ≤ C1 ≤ 8000 ppm, 4000 ppm ≤ C2 ≤ 10000 ppm) because the content of the additive element must be maintained above a certain level.

[0064]

[0065] In one specific example, the transition metal precursor of the present invention has a percentage of the distance where the center point and the gauge point are located, respectively L c , L e Let 0.4≤L c ≤0.6, 0.8≤L e It can be set to satisfy the condition <1.0.

[0066] There are various ways to implement such a structure, but one example is changing the timing of the change in the composition of the metal salt aqueous solution to form a discontinuity point during the co-precipitation process.

[0067] In particular, the above L e It is more preferable that is 0.9 or higher. This is because the additive element according to the present invention can generally be accompanied by the generation of microcracks and fine particles in relation to the shrinkage behavior of primary particles. If these effects occur excessively in the region adjacent to the surface, it can lead to a degradation of electrochemical performance, which is a chronic problem of the prior art with a high content of additive elements in the surface portion. In contrast, in the configuration according to the present invention, L e By setting to 0.8 or higher, particularly 0.9 or higher, the second region where the additive element exists at the highest concentration was limited to an internal location spaced a certain distance from the surface, and the content of the additive element in the third region was relatively reduced. Meanwhile, to ensure bulk structural stability, L c It is desirable that it be at least 0.4 or higher.

[0068]

[0069] In each of the aforementioned regions, it may be desirable for the content of the added element to be uniform regardless of the radius position within the region.

[0070] In other words, it is desirable to control the content of the additive element so that it is uniform within each region, without a concentration gradient, and so that the deviation between values ​​measured at different locations within the same region is maintained within a limited range. For example, when the average content of the additive element in regions 1 to 3 is denoted as C1, C2, and C3, the concentration within the region can be substantially uniform by designing the system so that there is almost no difference between the maximum and minimum values ​​of the additive element content measured in each region. Here, "uniform" means that while it is ideal for the additive element to exist at a completely constant content when distributed within a given region, a slight increase or decrease at the level of error is permitted due to technical limitations.

[0071] The present invention adopts a structure that establishes clear step differences at the regional level, rather than precisely controlling a fine content gradient across the entire radial section or a specific section as in a continuous concentration gradient structure. In this case, if a separate content gradient exists within each region, it is undesirable because it excessively reduces reproducibility. As the content of added elements within a region becomes more uniform, local variation in physical properties between primary particles or crystal grains belonging to the same region is reduced, thereby mitigating adverse effects.

[0072]

[0073] Meanwhile, some prior art has proposed a method of applying a so-called composition gradient by continuously or discontinuously varying the molar ratios of the transition metal composition itself, such as Ni, Co, and Mn, in the radial direction, instead of designing a separate distribution of additive elements as in the present invention. However, this method has the problem of an excessive number of design variables, as it requires controlling the optimal distribution of additive elements corresponding to each composition and designing stepwise gradients simultaneously and consistently. Therefore, it may be desirable not to include a concentration gradient of metals excluding additive elements.

[0074]

[0075] The average particle size of the transition metal precursor according to the present invention may preferably be in the range of 8 to 20 μm. If the average particle size is excessively small, the physical thickness of the discontinuity points defined by the distance percentage and the regions derived therefrom becomes very thin, making it difficult to structurally express the distribution of additive elements sufficiently. Conversely, if the average particle size is excessively large, the implementation of the additive element content distribution is easy and reproducibility is improved, but the overall packing density of the precursor decreases, making it difficult to contribute to the improvement of the performance of the cathode active material.

[0076] In the case of specific surface area and tap density, the BET specific surface area is 14 m² 2 It may be desirable for the specific surface area to be greater than or equal to g and the tap density to be greater than or equal to 1.8 g / cc. Generally, the specific surface area and tap density of the precursor and the cathode active material produced therefrom have a trade-off relationship. In the prior art, attempts were made to compensate for this by adjusting only the bulk composition or surface coating, but there were limitations in fundamentally resolving this. In contrast, the present invention can significantly mitigate the above relationship by controlling the internal structure of the particles to achieve reactivity, rather than relying solely on particle miniaturization or surface area maximization due to the existence of a discontinuity point based on the distance percentage.

[0077]

[0078] In one specific example, the transition metal precursor of the present invention may include the composition of the following chemical formula 1.

[0079] Ni a Mn b D c (OH)2(1)

[0080] In the above formula,

[0081] 0.6≤a<1.0, 0 <b≤0.3, 0<c≤0.1;

[0082] D is one or more selected from the group consisting of Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo and W.

[0083] In another specific example, the transition metal precursor of the present invention may include the composition of the following chemical formula 2.

[0084] Ni a' (Co x Mn 1-x ) b' D c' (OH)2(2)

[0085] In the above formula,

[0086] 0.6헯'<1, 0 <x≤0.05, 0<b'≤0.3, 0<c'≤0.1;

[0087] D is one or more selected from the group consisting of Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo and W.

[0088] In the composition of Chemical Formula 2 above, some of the Ni and / or Mn content is substituted with Co. Since Co has various oxidation states and readily combines with Li ions, it can stabilize the layered structure in place of the additive element. However, since Co reduces the Ni and / or Mn content by the amount of Co included in the transition metal precursor, it may be desirable to limit the Co content to the above range.

[0089] Meanwhile, since the cation mixing that generally reduces the capacity of Ni-based precursors or cathode active materials occurs more frequently as the Ni content increases, the effect may be more pronounced in High-Ni-based precursors containing 60 mol% or more, particularly 80 mol% or more, of Ni based on the total weight of the transition metal.

[0090]

[0091] The present invention also provides a positive electrode active material produced through a calcination reaction of a transition metal precursor and a lithium raw material, and a secondary battery comprising said positive electrode active material.

[0092] Since the method for manufacturing the positive electrode active material and the composition and manufacturing method of the secondary battery are known in the art, a detailed description thereof is omitted in this specification.

[0093] As explained above, the transition metal precursor of the present invention comprises a plurality of stepwise gradients having discontinuities in the content function according to the distance from the particle center, so that the anode active material manufactured using it can suppress the collapse of the layered structure during the insertion and extraction of Li ions during charging and discharging, thereby having the effect of excellent electrochemical properties such as lifespan characteristics.

[0094] FIG. 1 is a drawing disclosing the SEM-EDS measurement results of a first region in a transition metal precursor according to Example 1;

[0095] FIG. 2 is a drawing disclosing the SEM-EDS measurement results of a second region in a transition metal precursor according to Example 1;

[0096] FIG. 3 is a drawing showing the SEM-EDS measurement results of a third region in a transition metal precursor according to Example 1.

[0097] The present invention will be described further below with reference to embodiments thereof, but the scope of the invention is not limited by them.

[0098]

[0099] [Example 1]

[0100] An aqueous solution of complex transition metals containing nickel, cobalt, and manganese salts was prepared to 2.3 M by dissolving them in distilled water using NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O at a molar ratio of Ni:Co:Mn = 75:05:20. In addition, a 25 wt% aqueous sodium hydroxide solution was prepared as a pH adjuster and alkali source, and a 30 wt% aqueous ammonia solution was prepared as a metal ion complexing agent.

[0101] Additionally, an aqueous aluminate solution for Al addition, a 1M Al2(SO4)3 aqueous solution, and a 25 wt% sodium hydroxide aqueous solution were mixed in a volume ratio of 1.1:7 to prepare the solution. Subsequently, a 100L cylindrical overflow type co-precipitation reactor was prepared to produce a Ni-Co-Mn composite transition metal hydroxide precursor.

[0102] To minimize dissolved oxygen, 20 L of distilled water, 2 L of a 25 wt% sodium hydroxide aqueous solution, and 5 L of a 30 wt% ammonia solution were added to a 100 L cylindrical overflow type co-precipitation reactor in which nitrogen gas was constantly supplied at a rate of 3 L / min, and then the temperature was maintained at 60℃ with a stirring speed of 500 rpm.

[0103] A 2.3M aqueous complex transition metal salt solution was introduced into the above co-precipitation reactor at a flow rate of 0.6 L / min, while an aqueous sodium aluminate solution was introduced at a flow rate of 0.4 L / min. In addition, a 25 wt% aqueous sodium hydroxide solution and a 30 wt% aqueous ammonia solution were introduced into the reactor to maintain the pH of the reactor solution at 11.6±0.2 and the ammonia concentration at 3000±500 ppm at 25℃, thereby D 50Particles corresponding to the first region with a size of 6 μm were prepared. Then, an aqueous sodium aluminate solution was introduced at a flow rate of 0.9 L / min and synthesized until the average particle size reached 8 μm to prepare an intermediate in which the second region was formed. Finally, the flow rate of the aqueous sodium aluminate solution was introduced at 0.4 L / min and synthesized until the average particle size reached 10 μm to synthesize a composite transition metal hydroxide precursor in which the first to third regions were realized with two discontinuities.

[0104] A composite transition metal hydroxide powder was prepared by drying the synthesized precursor at 120°C for 20 hours through filtration and washing.

[0105]

[0106] [Example 2]

[0107] A composite transition metal hydroxide powder was prepared in the same manner as in Example 1, except that the sodium aluminate aqueous solution flow rates were changed to 0.25 L / min, 0.4 L / min, and 0.15 L / min, respectively, when sequentially preparing the first, second, and third regions.

[0108]

[0109] [Example 3]

[0110] A composite transition metal hydroxide powder was prepared in the same manner as in Example 1, except that the sodium aluminate aqueous solution flow rates were changed to 0.5 L / min, 0.8 L / min, and 0.4 L / min, respectively, when sequentially preparing the first, second, and third regions.

[0111]

[0112] [Example 4]

[0113] A composite transition metal hydroxide powder was prepared in the same manner as in Example 1, except that the sodium aluminate aqueous solution flow rates were changed to 0.2 L / min, 0.25 L / min, and 0.15 L / min, respectively, when sequentially preparing the first, second, and third regions.

[0114]

[0115] [Example 5]

[0116] A composite transition metal hydroxide powder was prepared in the same manner as in Example 1, except that the sodium aluminate aqueous solution flow rates were changed to 0.4 L / min, 0.5 L / min, and 0.35 L / min, respectively, when sequentially preparing the first, second, and third regions.

[0117]

[0118] [Example 6]

[0119] A composite transition metal hydroxide powder was prepared in the same manner as in Example 1, except that the sodium aluminate aqueous solution flow rates were changed to 0.3 L / min, 0.5 L / min, and 0.22 L / min, respectively, when sequentially preparing the first, second, and third regions.

[0120]

[0121] [Comparative Example 1]

[0122] An aqueous metal salt solution of NCM 75:5:20 Al at a concentration of 6000 ppm was continuously supplied to a 30L cylindrical reactor along with aqueous ammonia and caustic soda solutions, and while the ammonia concentration in the reactor was adjusted to 3000–5000 ppm and the pH to 12.1–12.5, a co-precipitation reaction was carried out at 60°C with a stirring speed of 500 rpm, resulting in an average particle size (D 50 ) was synthesized until it became 5 μm to produce a central particle corresponding to the first region.

[0123] Then, an aqueous metal salt solution with an NCM 75:5:20 Al composition of 3000 ppm was added and continuously supplied along with aqueous ammonia water and caustic soda solution to lower the pH to 11.6–11.8, and D 50 A precursor was prepared by synthesizing until it reached 10 μm, with a surface portion corresponding to a third region added to the central particle.

[0124] A composite transition metal hydroxide powder was prepared by drying the synthesized precursor at 120°C for 20 hours through filtration and washing.

[0125]

[0126] [Comparative Example 2]

[0127] A transition metal precursor was prepared in the same manner as Comparative Example 1, except that the Al input amounts in the center and surface portions were changed to 3000 ppm and 6000 ppm, respectively.

[0128]

[0129] [Comparative Example 3]

[0130] A transition metal precursor was prepared in the same manner as Comparative Example 1, except that the Al input amounts in the center and surface portions were changed to 8000 ppm and 4000 ppm, respectively.

[0131]

[0132] [Comparative Example 4]

[0133] A transition metal precursor was prepared using the same method as Comparative Example 1, except that the amount of Al input in the core and surface portions was set to 6000 ppm each.

[0134]

[0135] [Comparative Example 5]

[0136] A transition metal precursor was prepared in the same manner as Comparative Example 1, except that the amount of Al added during the formation of the core was 6000 ppm and no Al was added during the formation of the surface.

[0137]

[0138] [Comparative Example 6]

[0139] A transition metal precursor was prepared in the same manner as Comparative Example 1, except that Al was not added when forming the core and the amount of Al added when forming the surface was changed to 6000 ppm.

[0140]

[0141] [Comparative Example 7]

[0142] An aqueous metal salt solution of NCM 75:5:20 Al at a concentration of 6000 ppm was continuously supplied to a 30L cylindrical reactor along with aqueous ammonia and caustic soda solutions, and while the ammonia concentration in the reactor was adjusted to 3000–5000 ppm and the pH to 11.1–11.5, a co-precipitation reaction was carried out at 60°C with a stirring speed of 400 rpm, resulting in an average particle size (D 50 Synthesized until the thickness reached 5 μm to produce a central particle corresponding to the first region.

[0143] Then, an aqueous metal salt solution with an NCM 75:5:20 Al composition of 3000 ppm was added and continuously supplied along with aqueous ammonia water and caustic soda solution to lower the pH to 10.6–10.8, and D 50 A precursor was prepared by synthesizing until it reached 10 μm, with a surface portion corresponding to a third region added to the central particle. The synthesized precursor was dried at 120°C for 20 hours through filtration and washing to prepare a composite transition metal hydroxide powder.

[0144]

[0145] [Comparative Example 8]

[0146] A transition metal precursor was prepared in the same manner as Comparative Example 7, except that the Al input amounts in the center and surface portions were changed to 3000 ppm and 6000 ppm, respectively.

[0147]

[0148] [Comparative Example 9]

[0149] A transition metal precursor was prepared in the same manner as Comparative Example 7, except that the Al input amounts in the center and surface portions were changed to 8000 ppm and 4000 ppm, respectively.

[0150]

[0151] [Comparative Example 10]

[0152] A composite transition metal hydroxide powder was prepared in the same manner as in Example 1, except that the sodium aluminate aqueous solution flow rates were changed to 0.25 L / min, 0.4 L / min, and 0.5 L / min, respectively, when sequentially preparing the first, second, and third regions.

[0153]

[0154] [Comparative Example 11]

[0155] A composite transition metal hydroxide powder was prepared in the same manner as in Example 1, except that the sodium aluminate aqueous solution flow rates were changed to 0.15 L / min, 0.4 L / min, and 0.15 L / min, respectively, when sequentially preparing the first, second, and third regions.

[0156]

[0157] [Manufacture of Cathode Active Material]

[0158] A Li-transition metal mixed precursor powder was prepared by mixing LiOH with the transition metal precursors prepared in the above comparative examples and examples, respectively, at a molar ratio of 1.02, and then calcining the powder at 800°C for 18 hours to prepare an anode active material.

[0159]

[0160] [Lithium secondary battery manufacturing]

[0161] The above-described positive active material was mixed with Super-P, a conductive material, and PVdF, a binder, in a ratio of 93:5:2 (weight ratio) in N-methylpyrrolidone, a solvent, to prepare a positive active material slurry, which was then coated onto an aluminum current collector. After drying at 120°C, the electrode was rolled to produce an electrode. An electrode assembly was prepared by using lithium metal as the negative electrode along with the positive electrode prepared above, and interposing a porous polyethylene film as a separator between them. The electrode assembly was placed inside a battery case, and an electrolyte was injected into the battery case to produce a lithium secondary battery. At this time, as the electrolyte, a solution was prepared by dissolving 1.0 M concentration lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate and dimethyl carbonate (mixed volume ratio of EC / DMC = 1:1).

[0162]

[0163] [Experimental Example] Evaluation of Powder Characteristics and Electrochemical Properties

[0164] The BET specific surface area, tap density, and cycle characteristics of the transition metal precursors prepared in the above examples and comparative examples, respectively, were measured and are shown in Table 1 below.

[0165] In addition, to evaluate the cycle characteristics of the lithium secondary batteries manufactured above, the cells evaluated for initial charge / discharge were subjected to charge / discharge for 30 cycles (0.5C / 1C) at 45℃ within a voltage range of 2.5V to 4.25V, and after 30 charge / discharge cycles, 1 st 30 relative to the discharge capacity of the cycle th The capacity retention rate was calculated based on the discharge capacity ratio of the cycle and is shown together in Table 1 below.

[0166]

[0167] As shown in Table 1 above, while the precursors of Comparative Examples 1 to 9 have two regions distinguished by the content of added elements, the precursors of the Examples can be seen to have three regions.

[0168] Furthermore, the content of added elements in each region is 1.0 <C2 / C1≤2.0의 조건, 1.5≤C2 / C3≤2.5의 조건, 2000 ppm ≤ C3 ≤ C1 ≤ 8000 ppm의 조건, 4000 ppm ≤ C2 ≤ 10000 ppm의 조건을 모두 만족하는 것을 볼 수 있다. 일 예로, 실시예 1에 따른 전구체의 SEM-EDS 측정 결과가 개시되어 있는 도 1 내지 3을 참조하면, 도 1에서는 제 1 영역으로 설정된 부위, 도 2에서는 제 2 영역으로 설정된 부위, 도 3에서는 제 3 영역으로 설정된 부위를 각각 확인할 수 있고, 첨가원소인 Al이 제 1 영역에서는 0.64 wt% (약 6000 ppm), 제 2 영역에서는 0.79 wt% (약 8000 ppm), 제 1 영역에서는 0.38 wt% (약 4000 ppm)의 함량으로 존재하는 것도 확인되어, 상기 조건들을 만족하는 것이 실험적으로 입증된다.

[0169] This contrasts significantly with Comparative Examples 2, 4, 6, and 8, which have a high content of added elements, particularly on the particle surface.

[0170] In addition, the precursors of the examples have a BET specific surface area of ​​14 m² 2 It satisfies the condition of having a tap density of 1.8 g / cc or more and a BET specific surface area of ​​1,000 g / cc or more, and is compared with Comparative Examples 1 and 5, which have a small tap density, and Comparative Examples 7 to 9, which have a small tap density.

[0171] In particular, it can be confirmed that a secondary battery containing a positive electrode active material prepared from the precursors of the examples exhibits significantly superior cycle characteristics when compared to comparative examples.

[0172] In addition, Comparative Example 10 has C3≤C1 <C2 조건을 만족하지 못하는 바, 사이클 특성이 실시예들의 이차전지보다 많이 떨어지고, 비교예 11은 C2 / C1과 C2 / C3이 각각 3.0으로서 1.0<C2 / C1≤2.0와 1.5≤C2 / C3≤2.5의 조건을 만족하지 못하는 바, 탭 밀도(TD)가 1.8 g / cc에 이르지 못하고 사이클 특성도 실시예들의 이차전지보다 열위인 것을 확인할 수 있다.

[0173]

[0174] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. As a transition metal precursor for manufacturing a positive electrode active material, It includes an additive element which is one or more elements selected from the group consisting of Al, Zr, Mg, B, Ti, Zn, Sn, Ca, Ge, Ga, Mo, and W; When L is the percentage of the radial distance from the center of the precursor particle to the surface, and C is the content of the added element at that distance percentage, A transition metal precursor characterized by a one-to-one function having L as the domain and C as the codomain including a stair gradient in which at least two discontinuous L values ​​(hereinafter referred to as "discontinuity points") exist.

2. In Paragraph 1, When the discontinuity closest to the particle center among the above discontinuities is called the center point and the discontinuity closest to the particle surface is called the gauge point, A transition metal precursor characterized by being partitioned as follows based on the center point and the gauge point in the radial direction of the above particle: (i) A first region, which is the region from the center of the particle to the center point, (ii) a second region, which is the region from the above-mentioned center point to the above-mentioned indicator point, and (iii) A third region, which is the region from the above-mentioned point to the surface of the particle.

3. A transition metal precursor according to claim 2, wherein C1 to C3 have different values ​​when the average content of the additive element in the first, second, and third regions is denoted as C1, C2, and C3, respectively.

4. In claim 2, when the average content of the added element in the first, second, and third regions is denoted as C1, C2, and C3, respectively, C3 ≤ C1 <C2를 만족하는 것을 특징으로 하는 전이금속 전구체.

5. In Clause 4, 1.5 ≤ C2 / C3 ≤ 2.5, and 1.0 <C2 / C1≤2.0인 것을 특징으로 하는 전이금속 전구체.

6. A transition metal precursor according to claim 5, wherein C1 to C3 satisfy the following conditions: (i) 2000 ppm ≤ C3 ≤ C1 ≤ 8000 ppm (ii) 4000 ppm ≤ C2 ≤ 10000 ppm 7. In Clause 2, the percentage of distance where the center point and the gauge point are located is L, respectively. c , L e Let 0.4≤L c ≤0.6, 0.8≤L e A transition metal precursor characterized by being <1.

0.

8. A transition metal precursor according to claim 2, characterized in that, in each of the above regions, the content of the added element is uniform regardless of the radial position within the region.

9. A transition metal precursor according to claim 1, characterized in that it does not include a concentration gradient of metals excluding the additive element.

10. A transition metal precursor according to claim 1, characterized in that the average particle size of the transition metal compound particles is 8 to 20 μm.

11. In claim 1, the BET specific surface area is 14 m² 2 A transition metal precursor characterized by having a value of 1.8 g / cc or more and a tap density of 1.8 g / cc or more.

12. A positive electrode active material characterized by being manufactured through a calcination reaction between a transition metal precursor according to claim 1 and a lithium raw material.

13. A secondary battery characterized by including a positive electrode active material according to claim 12.

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