One-body active material particle and lithium secondary battery including same

Abstract

The present invention provides a one-body active material particle comprising: a core in the form of an independent primary particle; and a buffer layer formed on at least a part of the core, wherein the buffer layer comprises a sintering-promoting element for inducing the growth of a grain in the particle, and the sintering-promoting element is at least one element selected from rare earth elements.

Description

Single active material particle and lithium secondary battery containing the same

[0001] The present invention relates to a single active material particle and a lithium secondary battery including the same, and more particularly, to a single active material particle having a core in the form of a primary particle and a buffer layer including a sintering promoting element that induces growth of crystal grains within the particle, and a lithium secondary battery including the same.

[0002] Cathode active materials used in lithium secondary batteries typically have a secondary particle structure of several micrometers in size, formed by agglomeration of fine, submicron-sized primary particles. These secondary particle-structured cathode active materials suffer from the problem that battery performance deteriorates as the secondary particles break apart as the aggregated primary particles separate during repeated charge and discharge cycles. Because this problem stems from the structural characteristics of the secondary particles, it is difficult to address without structural modification. Therefore, a novel, single-body particle with a novel structure has been developed.

[0003] These single particles have a structure of a 'non-agglomerated single particle' rather than a 'structure of agglomerated primary particles', and since there is 'almost' no particle agglomeration, there is no particle separation due to charge and discharge, thereby solving the problem that occurs in secondary particle active materials. Here, the term 'almost' means that some agglomerated lumps that inevitably exist during the manufacturing of the novel single particle / powder are allowed. That is, since it is practically impossible for all particles to exist in a perfectly separated state due to technical limitations, some unintended agglomerated lumps may occur.

[0004] Unlike conventional secondary particles, the novel single particle has a particle size of several μm and does not have an aggregated structure, so there is no particle separation during charging and discharging, and thus it can fundamentally solve the problems that occur in secondary particle active materials.

[0005] However, unlike secondary particle active materials, it is very difficult to secure stable properties for single particle active materials, which is due to structural differences.

[0006] A representative problem arising from single-piece particles is the "oxygen desorption phenomenon." The degree of oxygen desorption is proportional to the firing temperature and nickel content. At low firing temperatures, even with increased nickel content, the degree of oxygen desorption is very low.

[0007] In general, high-Ni active materials (Ni 60 mol% or more) in the form of secondary particles have very little oxygen desorption because the sintering temperature during manufacturing is low at around 700 to 800°C. In particular, as the Ni content increases, the sintering temperature further decreases to around 700°C, so there is almost no oxygen desorption.

[0008] On the other hand, since the sintering temperature of single particles is high, such as 850-1000℃, the oxygen desorption phenomenon occurs significantly, and since it is impossible to manufacture a single particle structure at a low sintering temperature, there is a problem that it is difficult to improve the oxygen desorption phenomenon because the sintering temperature cannot be significantly lowered even when the Ni content is increased. This oxygen desorption phenomenon occurs mostly at the surface area of ​​the single particle.

[0009] Thus, single-piece particles requiring high sintering temperatures will face further challenges in producing high-Ni cathode active materials if the oxygen desorption phenomenon remains unresolved. For example, when the Ni content of a single-piece particle is less than 60%, the degree of oxygen desorption is not severe. However, when the Ni content exceeds 60%, the degree of oxygen desorption increases, and particularly when the Ni content exceeds 80%, it becomes very severe. However, the high sintering temperature makes this problem difficult to resolve.

[0010] Oxygen desorption creates excessive amounts of NiO, a rock salt structure, within the layered structure of the cathode active material, increasing lithium byproducts. Repeated charge / discharge cycles gradually increase NiO, leading to increased resistance. Furthermore, the increased lithium byproducts trigger various side reactions, ultimately degrading battery performance, including capacity loss. Therefore, addressing the oxygen desorption issue is crucial for commercializing single-cell active materials.

[0011] Therefore, there is a high need in the art for a technology that can fundamentally solve the problems of single particle cathode active materials.

[0012] The present invention aims to solve the problems of the prior art as described above and the technical tasks requested from the past.

[0013] The inventors of the present invention, after in-depth research and repeated various experiments, have developed a new type of single-body active material particle having a core in the form of a primary particle and a buffer layer containing a sintering promoting element. The sintering promoting element contained in the buffer layer suppresses structural collapse due to oxygen desorption by lowering the sintering temperature, and the buffer layer prevents side reactions of the electrolyte with respect to the core, thereby improving the lifespan and high-voltage stability, thereby completing the present invention.

[0014] Therefore, the single active material particle according to the present invention,

[0015] Comprising a core in the form of an independent primary particle and a buffer layer formed on at least a portion of the core;

[0016] The above buffer layer includes a sintering promoting element that induces the growth of grains within the particles;

[0017] The above sintering promoting element is characterized in that it is at least one element selected from among rare earth elements.

[0018]

[0019] The single active material particle of the present invention has a buffer layer containing a sintering promoting element as defined above on the core, and this buffer layer functions as an intermediate layer between the active material particle and the electrolyte to minimize core defects and preserve performance. Specifically, in the sintering process, the sintering promoting element with low diffusion is mainly distributed on the surface area of ​​the core, enabling the formation of particles with a larger grain size, or further lowering the sintering temperature required for the formation of the same grain size compared to the conventional one, thereby suppressing structural collapse caused by the oxygen desorption phenomenon, and the buffer layer formed by such a sintering promoting element can improve the deterioration of the active material life due to contact with the electrolyte, and is also effective in increasing high-voltage stability.

[0020]

[0021] In the present invention, 'sintering' means a process in which crystal grains within a particle undergo a thermal activation process to become a lump, i.e., a process in which the number of crystal grains decreases and the size increases.

[0022] Therefore, in the present invention, the term 'sintering' is used with a separate meaning from 'firing', which is heat treatment at a high temperature in an oxygen atmosphere, and firing can be understood as a method for manufacturing single particles, and sintering can be understood as an effect derived from the firing.

[0023] A sintering accelerating element is an element that accelerates the generation or growth of crystal grains through sintering, and plays a role in inducing 'Ostwald ripening' between crystal grains within a single particle. Here, Ostwald ripening refers to a phenomenon in which the surface energy of the particle acts as a driving force, causing small particles (corresponding to crystal grains in the present invention) to become smaller or disappear, while large particles become larger.

[0024] The inventors of the present application judged that an element that satisfies the conditions of having a larger ionic radius, longer oxygen bond length, and lower diffusion power than Ni, which is a major component of the positive electrode active material, would be suitable for inducing Ostwald ripening on the surface of a single particle, and based on this, selected a sintering-promoting element to be included in the buffer layer.

[0025] Since these sintering-promoting elements have lower diffusion power than general additive elements, they exist at a high ratio on the surface of single particles even after sintering, and can induce crystal grain growth within the particles while suppressing side reactions with the electrolyte.

[0026] The above term 'diffusion power' can be defined as duffusivity or diffusion rate, and the higher the diffusion power of the sintering promoting element, the deeper it can penetrate from the surface of a single particle toward the center, and the diffusion power is proportional to the sintering temperature or the diffusion coefficient of the sintering promoting element itself.

[0027] Therefore, the sintering promoting element has different diffusion degrees within a single particle depending on the sintering conditions and element selection, and may exist only in the buffer layer or in both the buffer layer and the core depending on the sintering conditions, and reduces the number of crystal grains and increases the average crystal grain size through Ostwald ripening.

[0028]

[0029] In relation to crystal growth, the present invention increases the surface energy of at least some crystal grains through a sintering-promoting element and intensifies the surface energy difference between crystal grains, thereby inducing the occurrence of the Ostwald ripening phenomenon and crystal grain growth, thereby resulting in an increase in the single-particle density of a single particle. Here, the term "single-particle density" refers to the degree to which a particle is close to a single body, and the higher the single-particle density, the fewer the number of crystal grains per particle and the larger the crystal grain size.

[0030] As explained above, due to the sintering promoting element, a larger grain size can be obtained at the same sintering temperature, or the sintering temperature required to form the same grain size can be relatively lowered, so that the problem of structural collapse can be significantly improved by suppressing the oxygen desorption phenomenon by the lowered sintering temperature.

[0031] Specifically, the active material in the form of a general secondary particle formed by agglomeration of primary particles has a relatively low sintering temperature during manufacturing compared to that of a single particle, so that the oxygen desorption phenomenon is very small, and in particular, as the Ni content increases, the sintering temperature decreases further, so that the oxygen desorption phenomenon hardly occurs. On the other hand, in the case of a single particle such as the present invention, such oxygen desorption phenomenon may be serious, but this problem can be solved by a sintering promoting element.

[0032]

[0033] In one specific example, the buffer layer may essentially include an inner buffer layer formed in a core-centered direction based on the core surface, and may optionally include an outer buffer layer formed in a core-outward direction.

[0034] The inner buffer layer can be set as a region formed by sintering promoting elements diffusing into the core, and the outer buffer layer can be set as a region formed by sintering promoting elements not diffusing but remaining outside the core.

[0035] Specifically, the internal buffer layer is formed inside the core based on the core surface, and does not define a separate layer shape surrounding the core, but rather means a shape of an 'area' where sintering promoting elements are mainly distributed within the core.

[0036] Conversely, the core also refers to a region where sintering promoting elements are not distributed or only diffuse in trace amounts, as the center of a single particle, and is not a separate region distinct from the internal buffer layer, and thus its effect is less than that of the internal buffer layer.

[0037] Whether these internal and external buffer layers are formed can be controlled by the sintering conditions of a sintering-promoting element with low diffusion power.

[0038] Specifically, when there is insufficient heat under sintering conditions, the sintering promoting element cannot diffuse into the core, so only an external buffer layer can be formed, and this external buffer layer also plays a role in suppressing an increase in resistance of the single particle.

[0039] On the other hand, when the amount of heat is sufficient or excessive under the sintering conditions, all of the sintering promoting elements can diffuse into the core to form only an internal buffer layer. In this case, the distance through which the sintering promoting elements diffuse from the core surface to the center is proportional to the amount of heat, and it promotes grain growth within a single particle, thereby suppressing the oxygen desorption phenomenon and stabilizing the structure.

[0040] Since the inner buffer layer is formed by the sintering promoting element diffusing from the core surface toward the center, it may contain a concentration gradient of the sintering promoting element, and if it is concentrated in a specific area within the core due to the limitation of diffusion power, it may have a somewhat discontinuous distribution based on that area.

[0041] Accordingly, the inner buffer layer may include a concentration gradient of sintering promoting elements that decreases from the core surface toward the center.

[0042]

[0043] The above outer buffer layer may have a structure that applies at least a portion of the outer surface of the core, or may have a structure that applies the entire surface.

[0044] These external buffer layers also have the effect of suppressing resistance increases by minimizing contact between the electrolyte and the core.

[0045]

[0046] Preferably, the buffer layer may include both an inner buffer layer and an outer buffer layer.

[0047] If both the inner and outer buffer layers are formed by appropriately controlling the sintering conditions, grain growth at the core surface is promoted, suppressing oxygen desorption and effectively inhibiting reactions with the electrolyte. It should be noted that the concentration of sintering-promoting elements may differ between the core core and the buffer layer.

[0048]

[0049] The rare earth element may be, for example, scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gb), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), tholium (Ym), ytterbium (Yb), lutetium (Lu), etc., and preferably cerium (Ce) or neodymium (Nd).

[0050]

[0051] In one specific example, the core and buffer layer may further comprise at least one element selected from the group consisting of Zr, Y, Ti, Si, Nb, Ba, Ta, and V.

[0052] These elements have a larger atomic radius than Ni and a higher diffusivity than sintering-promoting elements, and can maximize the grain growth effect together with sintering-promoting elements, so they can be considered a kind of 'complementary element' to sintering-promoting elements.

[0053] Therefore, when the above complementary element(s) are added together with a sintering promoting element, the material mobility through the grain boundary is improved, which further enhances the diffusion ability of the sintering promoting element and can enhance the Ostwald ripening effect. Additionally, the complementary element can also improve the Li diffusion within the active material.

[0054] The above-mentioned complementary elements have a higher diffusivity than the sintering-promoting elements, and thus can be relatively evenly distributed within a single particle, compared to the sintering-promoting elements, which are mainly distributed farther from the core center. In addition, the enhanced diffusivity of the sintering-promoting elements allows them to diffuse deeper into the single particle, thereby inducing grain growth over a wider area, and reducing the grain boundary area within the particle, thereby lowering resistance and improving life characteristics.

[0055] Since the above-mentioned supplementary elements should contribute to the flow of sintering promoting elements within the single particle, it is desirable for them to be present in the internal buffer layer. On the other hand, if there is a large amount of residual elements on the surface of the core, they may act as resistance and deteriorate the electrochemical properties.

[0056]

[0057] The above core may include, for example, a composition represented by the following chemical formula 1.

[0058] Li a (M b D1 c D2 d )O e (1)

[0059] In the above formula,

[0060] 0.95≤a≤1.1, 0 <b<1, 0≤c≤0.05, 0≤d≤0.05, 0<e≤4, c<d, 바람직하게는 a+b+c+d=2, e=2이며;

[0061] M is at least one selected from Ni, Co, and Mn;

[0062] D1 is a sintering promoting element which is at least one rare earth element;

[0063] D2 is at least one element selected from the group consisting of Zr, Y, Ti, Si, Nb, Ba, Ta, and V.

[0064] If the sintering promoting element penetrates deeply toward the core center based on sufficient heat, c>0, and the closer to the core center, the more difficult it is for the sintering promoting element to diffuse, so c=0 at the center.

[0065] When D2, a complementary element that improves material transport, is added, the content near the core center is D2>D1 (c) because D2 is distributed relatively evenly compared to D1. <d)의 조건을 만족할 수 있다.

[0066]

[0067] The above inner buffer layer may include, for example, a composition represented by the following chemical formula 2.

[0068] Li p (M q D1 r D2 s )O t (2)

[0069] In the above formula,

[0070] 0.95≤p≤1.1, 0 <q<1, 0<r≤0.05, 0≤s≤0.05, 0<t<4, r> s, preferably p+q+r+s=2, e=2;

[0071] M is at least one selected from Ni, Co, and Mn;

[0072] D1 is a sintering promoting element which is at least one rare earth element;

[0073] D2 is at least one element selected from the group consisting of Zr, Y, Ti, Si, Nb, Ba, Ta, and V.

[0074] In the composition of the inner buffer layer, the sintering promoting element penetrates into the interior of the single particle in the form of a substitution for the transition metal, and exists in the form of a lithium-transition metal compound, which may be similar even when the sintering promoting element is included in the core.

[0075] In the inner buffer layer close to the surface of the core, since it corresponds to the region immediately after the sintering promoting element starts to diffuse, when D2, a complementary element that is relatively evenly distributed within a single particle compared to the sintering promoting element, is added, the content in that region is D2.<D1 (r> s) can satisfy the condition.

[0076]

[0077] The above outer buffer layer may include, for example, a composition represented by the following chemical formula 3.

[0078] Li x D1 y O z (3)

[0079] In the above formula,

[0080] 0≤x≤1.1, 0 <y≤1, 0<t≤4

[0081] D1 is a sintering promoting element that is at least one of the rare earth elements.

[0082]

[0083] The outer buffer layer formed on the core surface is made of lithium-metal oxide (0 <x≤1.1) 또는 금속 산화물(x=0)일 수 있으며, 보족 원소인 D2는 그 분포가 확산에 기인하지 않기 때문에 입자 내부에 전반적으로 고르게 분포하며, 표면에는 남아있지 않는다. 따라서, 외부 버퍼층은 소결 촉진 원소(D1) 만을 포함하는 리튬-금속 산화물 또는 금속 산화물의 코팅층 형태일 수 있다.

[0084]

[0085] The average grain size of the core and buffer layers may be different.

[0086] Specifically, although there may be differences in the degree of distribution, the sintering promoting elements penetrate into the interior by diffusion from the core surface, and the grain size or grain size is proportional to the content of the sintering promoting elements in the corresponding region, so the grain sizes at the core center and the surface may be different.

[0087] The degree of grain growth is proportional to the content of sintering-promoting elements included in the relevant area, and due to the nature of sintering-promoting elements distributed by diffusion, the content is higher closer to the particle surface, so larger grains can be formed in the buffer layer compared to the core center.

[0088]

[0089] The above core may preferably have a composition including Ni of 60 mol% or more based on the total transition metal content.

[0090] Since the oxygen desorption phenomenon of a single particle mainly occurs in an active material having a Ni content of 60 mol% or more, the single active material particles of the present invention can exhibit a more significant improvement effect than nickel-based single particles. On the other hand, when the Ni content is smaller than the above size, it is difficult to secure a significant capacity, and the effect of suppressing the crystal grain growth and oxygen desorption phenomenon by the sintering promoting element may be minimal.

[0091]

[0092] In one specific example, the condition that the ratio of Ni content to the crystal grain size of the (003) plane during XRD analysis is 0.17 (mol% / nm) or less can be satisfied.

[0093] The single particle according to the present invention satisfies the condition that the ratio of the grain size and the Ni content within the particle is 0.17 (mol% / nm) or less due to the growth of the crystal grains by the sintering promoting element. The crystal grain size is proportional to the Ni content and the sintering temperature, but in the case of a general single particle to which a sintering promoting element is not added, the crystal grains do not grow sufficiently even when the Ni content increases, and this can be confirmed in the experimental results described later.

[0094] If the conditions defined above are not satisfied, that is, if the ratio of the Ni content to the grain size of the (003) plane exceeds 0.17 (mol% / nm), the grain growth rate according to the Ni content is low, so the oxygen desorption phenomenon cannot be effectively suppressed, which is not desirable.

[0095] The lowest value for the ratio of Ni content to grain size on the (003) plane can be set to 0.14 (mol% / nm) from the experimental results described later.

[0096]

[0097] In one preferred example, the sintering promoting element included in the core and inner buffer layer is 0.05 to 5 mol% based on the total transition metal content, and the sintering promoting element may be Ce.

[0098] When the content of the sintering promoting element is less than 0.05 mol%, the improvement effect is minimal even if a buffer layer is formed, whereas when it exceeds 5 mol%, the amount of heat required to form an internal buffer layer by diffusion becomes excessively high, and at the same amount of heat, the external buffer layer formed on the surface without penetrating into the core becomes excessively thick, which acts as resistance and may deteriorate the electrochemical performance. A more preferable content of the sintering promoting element may be in the range of 0.3 mol% to 1 mol%.

[0099] The content of sintering promoting elements included in the core and inner buffer layer may vary depending on the sintering conditions.

[0100] Specifically, if the sintering temperature is excessively high, excessive sintering-promoting elements may diffuse into the core, resulting in an overall uneven distribution of the sintering-promoting elements, which may weaken the effect. When adding the same amount of sintering-promoting elements, if the sintering temperature is excessively high, the amount of sintering-promoting elements diffused into the core increases and the amount remaining on the surface decreases, which may weaken the effect of suppressing oxygen desorption, which mainly occurs on the surface of the single particle. In addition, in this case, there may be insufficient sintering-promoting elements to form an external buffer layer, which may prevent the formation of an external buffer layer of a significant level.

[0101] On the other hand, when the sintering temperature is low, the sintering promoting element may not sufficiently diffuse into the core, resulting in the formation of an excessively thick external buffer layer, which may act as resistance and deteriorate the electrochemical properties.

[0102] Therefore, in order to form optimal internal and external buffer layers containing sintering-promoting elements and improve electrochemical properties to a desired level, it may be important to precisely control the sintering conditions, such as the content of the elements, as described above.

[0103]

[0104] The present invention also provides a positive electrode active material comprising the single active material particle and a lithium secondary battery comprising such positive electrode active material.

[0105] Since the composition of the positive electrode active material and the lithium secondary battery and the manufacturing method thereof are known in the art, a detailed description thereof is omitted in this specification.

[0106] As described above, the single-piece positive electrode particle according to the present invention exhibits the effect of improving the lifespan and high-voltage stability by suppressing structural collapse due to oxygen desorption phenomenon by lowering the sintering temperature through the sintering promoting element contained in the buffer layer, and by preventing the side reaction of the electrolyte with respect to the core through the buffer layer.

[0107] Figure 1 is an FE-SEM EDS image of the positive electrode active material of Example 3 in Experimental Example 1;

[0108] Figure 2 is an image based on Nano SIMS data for the positive electrode active material of Example 1 in Experimental Example 1;

[0109] Figures 3a to 3d are SEM images of the positive electrode active materials of Comparative Examples 1 and 2 and Examples 3 and 7 obtained in Experimental Example 2;

[0110] Figure 4 is a graph showing specific results of high-voltage stability performed on lithium secondary batteries each including the positive electrode active materials of Comparative Example 1 and Example 2 in Experimental Example 5.

[0111] Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention, but the scope of the present invention is not limited thereto.

[0112]

[0113] Comparative Example 1

[0114] Ni based on NCM composition 0.6 Co 0.1 Mn 0.3 In the production of a cathode active material, first, a nickel precursor, NiSO4, a cobalt precursor, CoSO4, and a manganese precursor, MnSO4, were added to water at a molar ratio of 0.6:0.1:0.3 to prepare a nickel-cobalt-manganese hydroxide precursor aqueous solution. While stirring the aqueous solution so that the raw materials were uniformly mixed, an aqueous sodium hydroxide solution was slowly added dropwise, and the reaction mixture was stirred for 5 hours to neutralize the precursor aqueous solution, thereby producing a nickel-cobalt-manganese hydroxide. 0.6 Co 0.1 Mn 0.3 (OH)2 was precipitated.

[0115] The above-mentioned precursor (nickel-cobalt-manganese hydroxide) powder was weighed with lithium carbonate (Li2CO3, ALB) at a Li / Metal = 1.03 ratio, placed in a Henschel 10L device, and stirred at 3000 rpm for 30 min to prepare a mixture.

[0116] The above mixture was placed in an alumina crucible and calcined at 950°C for 10 hours in an air atmosphere to produce a cathode active material with a single morphology and a high crystallinity with a developed layered structure. The produced cathode active material has the characteristic of being easily crushed by an external physical force, and thus, by high-speed crushing in an ACM crushing device, a single-crystal cathode active material with an average particle size of 3 to 5 μm was obtained.

[0117]

[0118] Comparative Example 2

[0119] A positive electrode active material was manufactured in the same manner as in Comparative Example 1, except that the sintering temperature was 980°C.

[0120]

[0121] Comparative Example 3

[0122] A cathode active material was manufactured in the same manner as in Comparative Example 1, except that the Ni-Co-Mn molar ratio of the precursor aqueous solution was 0.65: 0.05: 0.3.

[0123]

[0124] Comparative Example 4

[0125] A cathode active material was manufactured in the same manner as in Comparative Example 1, except that the Ni-Co-Mn molar ratio of the precursor solution was 0.8: 0.1: 0.1, lithium hydroxide (LiOH, SQM) was used instead of lithium carbonate as the lithium raw material to be weighed with the precursor, and the calcination temperature was 850°C.

[0126]

[0127] Comparative Example 5

[0128] A cathode active material was manufactured in the same manner as in Comparative Example 4, except that the molar ratio of Ni-Co-Mn in the precursor solution was 0.9: 0.05: 0.05 and the calcination temperature was 820°C.

[0129]

[0130] Example 1

[0131] A cathode active material was manufactured in the same manner as in Comparative Example 2, except that 0.3 mol% of CeO2 was added when measuring the precursor and lithium carbonate.

[0132]

[0133] Example 2

[0134] A cathode active material was manufactured in the same manner as in Comparative Example 1, except that 0.1 mol% of CeO2 was added when measuring the precursor and lithium carbonate.

[0135]

[0136] Example 3

[0137] A positive electrode active material was manufactured in the same manner as in Example 1, except that the sintering temperature was changed to 950°C.

[0138]

[0139] Example 4

[0140] A cathode active material was prepared in the same manner as in Example 3, except that Nd2O3 was added instead of CeO2.

[0141]

[0142] Example 5

[0143] A positive electrode active material was manufactured in the same manner as in Example 3, except that the amount of CeO2 added was changed to 1.0 mol%.

[0144]

[0145] Example 6

[0146] A positive electrode active material was manufactured in the same manner as in Example 1, except that 0.3 mol% of CeO2 was added and 0.5 mol% of ZrO2 was added simultaneously.

[0147]

[0148] Example 7

[0149] A positive electrode active material was manufactured in the same manner as in Example 3, except that 0.3 mol% of CeO2 was added and 0.5 mol% of ZrO2 was added simultaneously.

[0150]

[0151] Example 8

[0152] A cathode active material was manufactured in the same manner as in Example 3, except that the molar ratio of Ni-Co-Mn in the precursor solution was changed to 0.65: 0.05: 0.3.

[0153]

[0154] Example 9

[0155] A positive electrode active material was manufactured in the same manner as in Example 8, except that the sintering temperature was changed to 930°C.

[0156]

[0157] Example 10

[0158] A cathode active material was manufactured in the same manner as in Example 8, except that the Ni-Co-Mn molar ratio of the precursor solution was changed to 0.8: 0.1: 0.1, the calcination temperature was changed to 850°C, and lithium hydroxide was used instead of lithium carbonate.

[0159]

[0160] Example 11

[0161] A cathode active material was manufactured in the same manner as in Example 8, except that the Ni-Co-Mn molar ratio of the precursor solution was changed to 0.9: 0.05: 0.05, the calcination temperature was changed to 820°C, and lithium hydroxide was used instead of lithium carbonate.

[0162]

[0163] Manufacturing of lithium secondary batteries

[0164] In the above comparative examples and examples, the positive electrode active materials manufactured respectively were mixed with Super-P as a conductive agent and PVdF as a binder in a solvent, N-methylpyrrolidone, at a weight ratio of 93:5:2 to manufacture a positive electrode active material slurry, which was then applied onto an aluminum current collector. After drying at 120°C, the slurry was rolled to manufacture an electrode. An electrode assembly was manufactured by using lithium metal as an anode together with the positive electrode manufactured above and interposing a porous polyethylene film as a separator therebetween, and the electrode assembly was placed inside a battery case, and an electrolyte was injected into the battery case to manufacture a lithium secondary battery. At this time, the electrolyte used was lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1.0 M in an organic solvent composed of ethylene carbonate / dimethyl carbonate (EC / DMC mixing volume ratio = 1:1).

[0165]

[0166] Experimental Example 1: FE-TEM Measurement

[0167] The image obtained by performing FE-SEM EDS on the positive electrode active material manufactured in Example 3 under the following measurement conditions is shown in Fig. 1.

[0168] <Measurement conditions>

[0169] - Model: Themis Z

[0170] - Accelerating voltage: 300 kV

[0171] - Probe current @ 1nm (nA*) : 0.6

[0172] - System evergy resolution: 0.7 eV

[0173] -STEM resolution (nm): 0.136

[0174] - EDS-Scan rate: medium (30s), 5min.

[0175]

[0176] As shown in Fig. 1, it can be confirmed that Ce, a sintering promoting element, is concentrated and distributed in the surface layer to form a buffer layer. That is, through diffusion by high-temperature firing, the sintering promoting element penetrates from the surface into the core to form an internal buffer layer, and during high-temperature firing, excessive or surplus sintering promoting elements remain on the surface or remain on the surface through low-temperature firing to form an external buffer layer.

[0177]

[0178] In addition, Nano SIMS data on the element distribution from the surface to the center of a single particle in the positive electrode active material manufactured in Example 1 are shown in Fig. 2. Similarly, in Fig. 2, it can be confirmed that Ce is mainly distributed in the surface layer.

[0179]

[0180] Experimental Example 2: SEM Image

[0181] SEM images of the positive electrode active materials manufactured in Comparative Examples 1 and 2 and Examples 3 and 7 are shown in FIGS. 3a to 3d, respectively.

[0182] Figure 3a is an SEM image of the positive electrode active material of Comparative Example 1, Figure 3b is an SEM image of the positive electrode active material of Comparative Example 2, Figure 3c is an SEM image of the positive electrode active material of Example 3, and Figure 3d is an SEM image of the positive electrode active material of Example 7.

[0183] In order to compare the degree of particle growth according to the presence or absence of a sintering promoting element under the same composition (Ni:Co:Mn=60:10:30) and the same sintering temperature (950 degrees), when comparing Examples 3 and 7 with Comparative Example 1, it can be confirmed that the degree of particle growth is greatly improved in the Examples.

[0184] In addition, for comparison under the same composition (Ni:Co:Mn=60:10:30) and different firing temperatures (980°C vs. 950°C), when Examples 3 and 7 are compared against Comparative Example 2, it can be confirmed that Examples 3 and 7 show grain growth similar to or better than that of Comparative Example 2 fired at 980°C, even though they were fired at a relatively low temperature of 950°C. This shows that the required firing temperature for forming single particles can be lowered by promoting grain growth through the addition of a sintering promoting element.

[0185]

[0186] Experimental Example 3: XRD Measurement

[0187] The crystal grain sizes of the positive electrode active materials manufactured in Comparative Examples 1, 2, and 3 and Examples 3, 8, and 9 were measured under the following measurement conditions and are shown in Table 1 below.

[0188] <Measurement conditions>

[0189] - Model: X-Pert Pro MRD (PANalytical Philips)

[0190] - X-ray tube: Ceramic

[0191] - Power: 3 kW

[0192] - Range: 10 ~ 80'

[0193]

[0194] As shown in Table 1 above, when measuring the grain size, it can be confirmed that the positive electrode active material of the example to which the sintering promoting element was applied exhibits a significantly larger grain size under the same conditions.

[0195] Specifically, when Comparative Example 1 and Example 3 are compared with each other, it can be confirmed that single particles having a higher particle size (larger crystal grains) are realized by the sintering promoting element at the same sintering temperature (950 degrees).

[0196] Comparing Comparative Example 3 and Example 9, it can be confirmed that the particle size is improved due to the effect of the sintering promoting element, even though the sintering temperature of Example 9 (930 degrees) is lower.

[0197] Comparing Examples 3 and 8, it can be confirmed that the effect of the sintering promoting element is proportional to the Ni content, as the Ni content increases at the same sintering temperature (950 degrees), resulting in larger crystal grains.

[0198]

[0199] In addition, when the comparative examples and examples are compared with each other for the same Ni content, it can be confirmed that the crystal grain size of the examples to which the sintering promoting element is applied is larger, and therefore the ratio of the Ni content to the crystal grain size (mol% / nm) is smaller for the examples than for the comparative examples at the same Ni content. Meanwhile, the ratio tends to decrease as the Ni content increases, but when the sintering promoting element is not applied, there is a limit to the growth of the crystal grain size due to sintering even if the Ni content increases, and thus the ratio cannot be lowered below 0.17 mol% / nm.

[0200] On the other hand, the single particle according to the present invention can sufficiently grow crystal grains by a sintering promoting element, so that even if the Ni content increases, the ratio can be lowered to 0.17 mol% / nm or less.

[0201]

[0202] Experimental Example 4: Electrochemical Characteristics Evaluation

[0203] For each lithium secondary battery manufactured above, charging and discharging were performed at a rate of 0.1C and cut-off conditions of 4.3 to 4.5 V (charge) and 2.5 V (discharge), and the resistance was calculated by dividing the applied current by the voltage change between 0 and 70 seconds from the start of discharge (V / I=R).

[0204] In addition, the lifespan and resistance increase rate were measured by repeating the cycle 50 times at 45°C with a charge rate of 0.5C and a discharge rate of 1.0C and a cut-off condition of 4.3-4.5 V (charge) and 2.5 V (discharge).

[0205] The above results are shown in Table 2 below.

[0206]

[0207] The following can be confirmed through the results in Table 2 above.

[0208] First, as seen in Comparative Examples 3 to 5, as the Ni content increases, the resistance and life characteristics deteriorate.

[0209] Second, Example 1 relates to a cathode active material in which all sintering-promoting elements form an internal buffer layer through high-temperature firing. Compared to Comparative Example 2, which was fired at the same temperature (980°C), the sintering-promoting elements that formed an internal buffer layer improved structural stability, thereby extending the lifespan. On the other hand, since there is no external buffer layer, the resistance increase rate (△DCIR) is inferior to other examples having an external buffer layer.

[0210] Third, Examples 2 to 5 and 7 relate to positive electrode active materials fired at an appropriate temperature (950°C) capable of forming both internal and external buffer layers. Based on the composition, it is expected that the lower the firing temperature, the higher the ratio of the external buffer layer, and the higher the firing temperature, the higher the ratio of the internal buffer layer.

[0211] Fourth, when Example 2 and Comparative Example 2 are compared with each other, it can be confirmed that the sintering temperature can be lowered (980°C → 950°C) to achieve the same performance even with a trace amount (0.1 mol%) of a sintering promoting element. In addition, when Example 2 and Comparative Example 1 are compared with each other, the life characteristics are superior even at the same sintering temperature (950°C) due to the addition of a sintering promoting element, which can be inferred that oxygen desorption is suppressed.

[0212] Fifth, through a comparison of Examples 2 and 3, it can be confirmed that the life characteristics are improved as the content of the sintering promoting element increases, and through the results of Example 4, it can be confirmed that the electrochemical characteristics are improved according to Nd in addition to Ce.

[0213]

[0214] Sixth, when comparing Examples 2, 3, and 5, it can be confirmed that the electrochemical characteristics change according to the amount of Ce added at the same sintering temperature (950℃). Example 2, to which 0.1 mol% Ce was added, can be confirmed to have improved life characteristics due to the internal buffer layer, but is inferior to Examples 3 and 5 due to the low Ce content. In addition, Example 5, to which 1.0 mol% Ce was added, can secure life characteristics at the same level as Example 3, but it can be confirmed that it is inferior in terms of resistance because the external buffer layer is formed thicker. That is, when forming a buffer layer including a sintering promoting element according to the present invention, the sintering temperature and the amount of sintering promoting element added must be appropriately controlled to reach the desired levels of both resistance and life characteristics.

[0215]

[0216] Seventh, referring to the results of Examples 6 and 7, in which Zr, a complementary element that enhances diffusion ability, was added while the sintering promoting element formed a buffer layer, a comparison between Examples 6 and 1 shows that, at the same sintering temperature (980°C), when Zr is simultaneously added, the efficiency and lifespan characteristics are superior to Example 1, in which the sintering promoting element was added alone, even if the sintering promoting element only forms an internal buffer layer. In addition, a comparison between Examples 7 and 1 shows that, when the sintering promoting element and Zr are simultaneously added, the sintering temperature required to achieve the same or superior level of electrochemical characteristics can be lowered. In addition, a comparison between Examples 3 and 7 shows that, for the same sintering promoting element content, Zr, a complementary element, enhances the diffusion ability of the sintering promoting element, thereby achieving superior lifespan characteristics. Furthermore, a comparison between Examples 6 and 7 shows that, in Example 7, in which both the internal and external buffer layers are formed, the resistance characteristics are superior to those in Example 6, in which only the internal buffer layer is formed.

[0217]

[0218] Eighth, in terms of comparing the characteristics according to the Ni content under the same conditions, it can be confirmed through a mutual comparison of Comparative Example 3 and Example 8 that the life characteristics are improved by adding a sintering promoting element at the same sintering temperature (950 degrees), and through a mutual comparison of Comparative Example 3 and Example 9 that the life characteristics of Example 9 are superior even though the sintering temperature is lowered further compared to Comparative Example 3.

[0219]

[0220] Ninth, in the examples, it can be confirmed that the Ni content and the resistance increase rate are proportional, but the resistance increase is suppressed compared to the comparative examples corresponding to each composition.

[0221]

[0222] Experimental Example 5: Continuous Charging Test Method

[0223] For lithium secondary batteries manufactured based on the positive electrode active materials of Comparative Example 1 and Example 2, high-voltage stability was verified by maintaining the batteries at a charging voltage of 4.7 V and an environment of 70°C for 300 hours. The results are shown in Fig. 4.

[0224] As shown in Fig. 4, it can be confirmed that the lithium secondary battery including the positive electrode active material of Example 2 exhibits superior high-voltage stability in a high-temperature and high-voltage environment compared to the positive electrode active material of Comparative Example 1.

[0225]

[0226] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Comprising a core in the form of an independent primary particle and a buffer layer formed on at least a portion of the core; The above buffer layer includes a sintering promoting element that induces the growth of grains within the particles; A single active material particle characterized in that the above sintering promoting element is at least one element selected from rare earth elements.

2. In the first paragraph, the buffer layer, It essentially includes an internal buffer layer formed in the direction of the core center based on the core surface, A single-piece active material particle characterized by optionally including an outer buffer layer formed in an outer direction of the core.

3. A single active material particle, characterized in that the inner buffer layer comprises a concentration gradient of a sintering promoting element that decreases from the core surface toward the center.

4. A single active material particle characterized in that, in the second paragraph, the external buffer layer is applied to at least a portion of the outer surface of the core.

5. A single active material particle according to claim 2, characterized in that the buffer layer includes both an inner buffer layer and an outer buffer layer.

6. A single active material particle characterized in that in paragraph 1, the rare earth element is scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gb), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), tholium (Ym), ytterbium (Yb), and lutetium (Lu).

7. A single active material particle, characterized in that the rare earth element in claim 6 is cerium (Ce) or neodymium (Nd).

8. A single active material particle according to claim 1, characterized in that the core and buffer layer further comprise at least one element selected from the group consisting of Zr, Y, Ti, Si, Nb, Ba, Ta, and V.

9. In the first paragraph, the core is a single active material particle characterized in that it comprises a composition of the following chemical formula 1: Li a (M b D1 c D2 d )O e (1) In the above formula, 0.95≤a≤1.1, 0 <b<1, 0≤c≤0.05, 0≤d≤0.05, 0<e≤4, c<d; M is at least one selected from Ni, Co, and Mn; D1 is a sintering promoting element which is at least one rare earth element; D2 is at least one element selected from the group consisting of Zr, Y, Ti, Si, Nb, Ba, Ta, and V.

10. In the second paragraph, a single active material particle characterized in that the inner buffer layer comprises a composition of the following chemical formula 2: Li p (M q D1 r D2 s )O t (2) In the above formula, 0.95≤p≤1.1, 0 <q<1, 0<r≤0.05, 0≤s≤0.05, 0<t<4, r> s; M is at least one selected from Ni, Co, and Mn; D1 is a sintering promoting element which is at least one rare earth element; D2 is at least one element selected from the group consisting of Zr, Y, Ti, Si, Nb, Ba, Ta, and V.

11. In the second paragraph, a single active material particle characterized in that the external buffer layer comprises a composition of the following chemical formula 3: Li x D1 y ON z (3) In the above formula, 0≤x≤1.1, 0 <y≤1, 0<t≤4 D1 is a sintering promoting element, which is at least one rare earth element.

12. A single active material particle characterized in that the average grain sizes of the core and buffer layer are different in the first paragraph.

13. In the first paragraph, the core is a single active material particle containing Ni of 60 mol% or more based on the total transition metal content.

14. A single active material particle characterized in that, in the 13th paragraph, the ratio of the Ni content to the crystal grain size of the (003) plane during XRD analysis is 0.17 (mol% / nm) or less.

15. A single active material particle in the first paragraph, wherein the sintering promoting element included in the core and buffer layer is 0.05 to 5 mol% based on the total transition metal content.

16. A cathode active material characterized by comprising a single active material particle according to Article 1.

17. A lithium secondary battery characterized by including a positive electrode active material according to Article 16.

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