A modified ternary material, its preparation method and use

Abstract

The present invention belongs to the technical field of electrode materials. The present invention provides a modified ternary material, a preparation method thereof and uses. The preparation method includes mixing a ternary material matrix with a non-cobalt metal source to form a non-cobalt metal superficial doping region, obtaining a first modified material; then mixing with a cobalt source and performing a second sintering to form a cobalt gradient doping region with a decreasing cobalt element concentration, obtaining a second modified material; and finally mixing with a coating agent and performing a third sintering to form a coating layer on the surface of the second modified material, obtaining the modified ternary material. By first preparing the non-cobalt metal superficial doping region and using the non-cobalt metal elements enriched in the shallow surface layer position of the ternary material matrix as a barrier for subsequent cobalt element doping, the present invention effectively reduces the incorporation depth of cobalt elements, and further constructs a bulk doping structure with a more significant cobalt concentration gradient, which is beneficial to further improving the power performance and thermal stability of the ternary material matrix.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and relates to a modified ternary material, a preparation method thereof, and uses thereof. Background Art

[0002] The lithium nickel cobalt manganese oxide cathode material, also called ternary material, has the advantages of high energy density and good cycling performance, and is one of the most promising cathode materials for lithium-ion batteries at present.

[0003] With the continuous warming of the global electric vehicle market in recent years, the demand for ternary lithium-ion batteries has increased greatly. However, in the situation of increasingly fierce global competition for cobalt resources and the continuous increase in the price of cobalt raw materials, the trend of low cobalt content in ternary materials is becoming more and more obvious. Although reducing the content of cobalt element can effectively control the cost, since the cobalt element plays an important role in stabilizing the layered structure of the material, suppressing lithium-nickel mixing, and enhancing the ionic conductivity of the cathode material, the low-cobalt single-crystal ternary cathode material has problems such as poor rate performance and rapid increase in cycling DCR, and cannot meet the current requirements of electric vehicles for lithium-ion batteries.

[0004] Currently, most of the low-cobalt routes reduce the cobalt content at the precursor (such as cobalt manganese hydroxide) end, and then compensate for the defects of poor battery cycling performance and high internal resistance caused by low-cobalt materials through bulk doping of other elements (such as Zr doping) and surface modification (such as Al coating) in the subsequent process. There is also a strategy of post-compensating cobalt at the cathode end. For example, CN112750999A discloses a cobalt-coated ternary cathode material and a preparation method thereof, which roast a high-nickel cobalt-free cathode material intermediate and a nano cobalt-containing compound, and form a cobalt-containing compound on the outer surface of the high-nickel cobalt-free multi-component cathode material intermediate. By coating cobalt element on the surface, the material structure can be stabilized.

[0005] In fact, the improvement effect of the cobalt coating method on the material performance is closely related to the gradient structure formed by cobalt element inside the particle bulk phase. For example, the conventional pyrometallurgical coating used in CN112750999A cannot accurately control the Co coating gradient structure. When the temperature is too high, Co tends to be incorporated into the bulk phase, which can neither reduce the total content of Co nor form an obvious gradient distribution effect. When the coating temperature is too low, the cobalt element tends to stagnate on the material surface, only forming a coating layer, and its own improvement amplitude for the material performance is relatively limited.

[0006] Therefore, it is still necessary to develop and research the low-cobalt ternary material solution to accurately control and exert the optimization effect of the cobalt element gradient distribution, so as to effectively improve the energy density and cycling performance of the modified ternary material. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a modified ternary material, its preparation method and use. The preparation method includes mixing a ternary material matrix with a non-cobalt metal source to form a non-cobalt metal superficial doping region, obtaining a first modified material; then mixing with a cobalt source and performing a second sintering to form a cobalt gradient doping region with a decreasing cobalt element concentration, obtaining a second modified material; finally, mixing with a coating agent and performing a third sintering to form a coating layer on the surface of the second modified material, obtaining the modified ternary material. By first preparing the non-cobalt metal superficial doping region and using the non-cobalt metal element with a larger ionic radius enriched in the shallow surface layer position of the ternary material matrix as a barrier for subsequent cobalt element doping, the incorporation depth of cobalt elements is effectively reduced, and then a bulk doping structure with a more significant cobalt concentration gradient is constructed, which is beneficial to further improving the power performance and thermal stability of the ternary material.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a preparation method of a modified ternary material, including the following steps:

[0010] (1) Mixing a ternary material matrix with a non-cobalt metal source and performing a first sintering to form a non-cobalt metal superficial doping region from the surface to the inside of the ternary material matrix, obtaining a first modified material; the ionic radius of the non-cobalt metal element is larger than that of the cobalt element;

[0011] (2) Mixing the first modified material with a cobalt source and performing a second sintering to form a cobalt gradient doping region with a decreasing cobalt element concentration from the surface to the inside of the first modified material, obtaining a second modified material;

[0012] (3) Mixing the second modified material with a coating agent and performing a third sintering to form a coating layer on the surface of the second modified material, obtaining the modified ternary material.

[0013] In the preparation method of the present invention, the non-cobalt metal source with a larger metal ion radius is first sintered with the ternary material matrix to preferentially and directionally incorporate the non-cobalt metal element with a larger corresponding ion radius into the lattice of the ternary material matrix, and the doping depth is located in the shallow surface layer to form a barrier to block the subsequent cobalt doping. Based on this, during the second sintering, the incorporation depth of cobalt elements can be effectively reduced, and more cobalt can be restricted to the shallow surface layer, thus having the characteristics of high cobalt concentration, fast cobalt concentration gradient change, and large gradient difference in the shallow surface layer, that is, the cobalt concentration gradient in the shallow surface area is more obvious by itself, while in the non-shallow surface area (i.e., from the boundary of the shallow surface layer to the center of the particle), the cobalt concentration gradient changes slowly and the gradient difference is small. Therefore, overall, although cobalt is still bulk doping, due to the difference in the gradient structure in specific regions, the overall cobalt concentration gradient structure (i.e., the cobalt gradient doping region) is more significant. It can be seen that this specific cobalt concentration gradient structure is different from the structure with a uniform change in cobalt concentration gradient from the particle center to the surface manufactured by the conventional cobalt coating process.

[0014] Based on the specific cobalt concentration gradient structure formed by the present invention, since the cobalt element concentration is relatively high in the shallow surface area, especially on the surface, it can improve the ionic conductivity of the material, thereby reducing the material impedance and increasing the energy density; at the same time, the cobalt concentration gradient doping structure formed by the whole particle is also beneficial to improving the cycling performance. On this basis, the present invention performs coating through the third sintering to repair the surface of the material and obtain a modified ternary material with a complete coating layer. This coating layer can not only improve the ion transport rate but also reduce the side reaction between the particle and the electrolyte, preventing the cobalt concentration gradient distribution from being destroyed, so as to ensure that the gradient-doped cobalt element plays its due role. The preparation method has a simple process, is completely compatible with the existing production line mass production equipment, is easy to control during the production process, and is suitable for large-scale mass production.

[0015] It should be emphasized that if the shallow surface layer doping of non-cobalt metal elements is not carried out and the ternary material matrix is directly doped with cobalt, under the condition that other process conditions are the same, the incorporation depth of cobalt elements will increase, and the difference in the overall cobalt concentration gradient will decrease, resulting in a smaller improvement in the energy density and impedance performance of the material; at this time, in order to reduce the incorporation depth of cobalt elements, the sintering (i.e., the second sintering) temperature is often selected to be lowered. However, due to the low temperature, some cobalt elements will stagnate on the surface or surface layer of the material and cannot effectively penetrate into the bulk phase. These cobalt elements have high activity and will cause serious deterioration of the high-temperature storage gas generation and charge retention rate performance of the battery cell. Or rather, the existing technical methods cannot well balance the contradiction between the too deep incorporation depth of cobalt and the cobalt staying on the surface or surface layer of the particle. The present invention gives an effective improvement solution to the above problems, can better control the gradient doping of cobalt, and further improves the electrochemical performance of the modified ternary material.

[0016] It should also be noted that the doping of non-cobalt metal elements in the shallow surface layer means that they are not simply attached to the particle surface. The addition amount of non-cobalt metal elements is small, the doping depth from the surface is shallow, and there is no need to limit that the non-cobalt metal elements must also form a concentration gradient structure. The ionic radius of the non-cobalt metal element should be larger than that of the cobalt element, otherwise the incorporation of cobalt element cannot be effectively inhibited.

[0017] It should also be noted that in step (3) of the preparation method of the present invention, forming the coating layer has no influence on the already formed cobalt concentration gradient distribution. If only steps (1) and (2) are carried out, the obtained second modified material also has advantages compared with the ternary material matrix with uniform bulk doping of cobalt in the prior art, especially in terms of cycle and storage performance. Considering the overall performance of the obtained modified ternary material, especially the optimization of the capacity performance, it is more important to carry out step (3) to form the coating layer.

[0018] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following technical solutions, the technical purposes and beneficial effects of the present invention can be better achieved and realized.

[0019] As a preferred technical solution of the present invention, in step (1), the non-cobalt metal elements in the non-cobalt metal source include at least one of W, Mo or Nb.

[0020] Preferably, the non-cobalt metal source includes oxides.

[0021] Preferably, the particle size D of the non-cobalt metal source 50 is 0.02 - 1 μm, such as 0.02 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0022] In the present invention, the particle size D of the material 50 can be measured by a Malvern laser particle size analyzer.

[0023] Preferably, the mass ratio of the non-cobalt metal element in the non-cobalt metal source to the ternary material matrix is (0.0005~0.005):1, such as 0.0005:1, 0.0008:1, 0.001:1, 0.0013:1, 0.0015:1, 0.0018:1, 0.002:1, 0.0023:1, 0.0025:1, 0.0028:1, 0.003:1, 0.0033:1, 0.0035:1, 0.0038:1, 0.004:1, 0.0043:1, 0.0045:1, 0.0048:1 or 0.005:1, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0024] In the present invention, when the doping amount of the non-cobalt metal element is too small, it cannot effectively prevent the doping of the cobalt element, and an ideal cobalt concentration gradient structure cannot be obtained; while when the doping amount is too large, it will affect the kinetic performance of the material, and the energy density and initial DCR will deteriorate to a certain extent.

[0025] Preferably, the ternary material matrix includes a nickel-cobalt-manganese ternary material with the chemical formula Li(Ni x Co y Mn z )O 2 , 1>x≥0.6, such as x can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.95, etc.; 0.2≥y>0, such as y can be 0.2, 0.18, 0.15, 0.13, 0.1, 0.08, 0.06, 0.04, 0.02 or 0.01, etc.; 0.4≥z>0, such as z can be 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, 0.1, 0.05, 0.03 or 0.01, etc., and x + y + z = 1, but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0026] It should be noted that the preparation method of the present invention is mainly aimed at nickel-cobalt-manganese ternary materials with low cobalt (0.2≥y>0). However, the purpose of the present invention is to form a concentration gradient distribution of cobalt elements. Therefore, it can also play a certain degree of optimization effect on other types of nickel-cobalt-manganese ternary materials, such as NCM523. Under the condition of understanding the intention and purpose of the present invention, reasonable selection can be made according to actual needs.

[0027] Preferably, the method for preparing the ternary material matrix includes mixing a lithium source with a nickel-cobalt-manganese hydroxide precursor and calcining in an oxygen-containing atmosphere to obtain the ternary material matrix.

[0028] The present invention does not specifically limit the specific preparation method of the ternary material matrix, and preferably the high-temperature solid-phase sintering method commonly used in industry. In this high-temperature solid-phase sintering method, the ternary material matrix is mixed with a non-cobalt metal source for the first sintering to achieve the doping of the non-cobalt metal source in the shallow surface layer. It is not possible to mix and sinter the non-cobalt metal source with the ternary material matrix precursor (such as nickel cobalt manganese compound) in advance during the stage of synthesizing the ternary material matrix. In this way, due to the relatively high pre-sintering temperature for synthesizing the ternary material matrix, the non-cobalt metal elements will directly enter the bulk center, and it is impossible to control their distribution only in the shallow surface layer, and thus it is impossible to play a blocking role in the subsequent doping of cobalt elements, and the concentration gradient doping effect of cobalt elements cannot be formed.

[0029] Preferably, the lithium source includes at least one of lithium carbonate, lithium hydroxide or lithium nitrate; the nickel cobalt manganese hydroxide precursor includes Ni x Co y Mn z (OH) 2 , 1>x≥0.6, 0.2≥y>0, 0.4≥z>0, and x + y + z = 1. For example, x can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.95, etc.; 0.2≥y>0, for example, y can be 0.2, 0.18, 0.15, 0.13, 0.1, 0.08, 0.06, 0.04, 0.02 or 0.01, etc.; 0.4≥z>0, for example, z can be 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, 0.1, 0.05, 0.03 or 0.01, etc., and x + y + z = 1, but it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0030] Preferably, the molar ratio of lithium element in the lithium source to the transition metal element in the nickel cobalt manganese oxide is (1.00~1.08):1. For example, 1.00:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1 or 1.08:1, etc., but it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0031] Preferably, the temperature of the calcination is T 0 , T 0= 700 - 1000 °C, such as 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C or 1000 °C, etc., the time is 6 - 15 h, such as 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h or 15 h, etc., the oxygen concentration in the oxygen-containing atmosphere is 70% - 100%, such as 70%, 75%, 80%, 85%, 90%, 95% or 100%, etc., but not limited to the listed values, other unlisted values within the above value range are equally applicable.

[0032] As a preferred technical solution of the present invention, in step (1), the temperature of the first sintering is T 1 , T 1 = 700 - 900 °C, such as 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C, 780 °C, 800 °C, 820 °C, 850 °C, 880 °C or 900 °C, etc., the time is 4 - 15 h, such as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h or 15 h, etc., but not limited to the listed values, other unlisted values within the above value range are equally applicable.

[0033] If the sintering temperature in step S1 is too high, more metal elements will enter the bulk center, and then cannot hinder the further incorporation of cobalt elements in the subsequent step S2, and thus a material with the expected cobalt concentration gradient structure cannot be obtained. If the sintering temperature in S1 is too low, non-cobalt elements tend to stay on the surface of the ternary material matrix in the form of metal oxides, and also cannot effectively hinder the further incorporation of cobalt elements.

[0034] As a preferred technical solution of the present invention, in step (1), the coverage range of the non-cobalt metal superficial doping region starts from the surface of the ternary material matrix until the position of 80% - 99% of the center to the surface of the ternary material matrix, such as 80%, 83%, 85%, 88%, 90%, 93%, 95%, 98% or 99%, etc., that is, this position is the boundary of the non-cobalt metal superficial doping region inside the particle, but not limited to the listed values, other unlisted values within the above value range are equally applicable.

[0035] In the present invention, the non-cobalt metal is doped in the shallow surface layer. The thickness of the shallow surface layer or the depth of the non-cobalt metal element doping starts from the surface until the position of 80% - 99% of the center to the surface of the material, and there is doping of non-cobalt metal elements in this part. However, the boundary position cannot be 100%, that is, the non-cobalt metal elements cannot only adhere to the surface, but must be incorporated into the shallow surface layer.

[0036] As a preferred technical solution of the present invention, in step (2), a flux is used to mix with the first modification material and the cobalt source, and then the second sintering is carried out.

[0037] Preferably, the flux includes a compound containing at least one of Li, B, P or F.

[0038] Preferably, the flux includes lithium carbonate (Li 2 CO 3 ), lithium hydroxide (LiOH), aluminum fluoride (AlF 3 ), lithium fluoride (LiF), boron oxide (B 2 O 3 ), phosphoric acid (H 3 PO 4 ), or lithium phosphate (Li 3 PO 4 ) or at least one of them.

[0039] Preferably, the mass ratio of the flux to the cobalt source is (0.01~0.6):1, such as 0.01:1, 0.05:1, 0.08:1, 0.1:1, 0.13:1, 0.15:1, 0.18:1, 0.2:1, 0.23:1, 0.25:1, 0.28:1, 0.3:1, 0.33:1, 0.35:1, 0.38:1, 0.4:1, 0.43:1, 0.45:1, 0.48:1, 0.5:1, 0.53:1, 0.55:1, 0.58:1 or 0.6:1, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0040] Preferably, the cobalt source includes cobalt hydroxide (Co(OH) 2 ), cobalt oxyhydroxide (CoOOH) or cobalt tetroxide (Co 3 O 4 ) or at least one of them.

[0041] Preferably, the particle size D 50 of the cobalt source is 0.05~1.2μm, such as 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm or 1.2μm, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0042] Preferably, the mass ratio of cobalt element in the cobalt source to the first modification material is (0.005~0.03):1, such as 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, 0.011:1, 0.012:1, 0.013:1, 0.014:1, 0.015:1, 0.016:1, 0.017:1, 0.018:1, 0.019:1, 0.02:1, 0.022:1, 0.024:1, 0.026:1, 0.028:1 or 0.03:1, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0043] As a preferred technical solution of the present invention, in step (2), the temperature of the second sintering is T 2 , T 2 =650~850°C, such as 650°C, 660°C, 680°C, 700°C, 720°C, 740°C, 750°C, 780°C, 800°C, 820°C or 850°C, etc., and the time is 4~15h, such as 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0044] It should be noted that in the present invention, the concentration gradient distribution of cobalt element is affected not only by the surface doping of non-cobalt metals, but also by the temperature of the second sintering. However, the temperature of the second sintering is related to the specific selection of the ternary material matrix. When the component content of the ternary material matrix changes, the most suitable temperature of the second sintering will change within 650~850°C. Therefore, reasonable adjustment and selection should be made.

[0045] Generally, T1>T2 °C, preferably T1-T2>40 °C, such as T 1 -T 2 is 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C, 60°C, 63°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C or 80°C, etc., but not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0046] As a preferred technical solution of the present invention, in the second modified material, the concentration of cobalt element on the surface is denoted as a, the concentration of cobalt element at 80% of the position from the center to the surface is denoted as b, and the concentration of cobalt element at 50% of the position from the center to the surface is denoted as c; the concentration of cobalt element in the ternary material matrix is denoted as d; the cobalt element concentration refers to the percentage of the amount of substance of cobalt element in the total amount of substance of nickel, cobalt and manganese elements. Then, 10 > (a - b) / (c - d) > 3. For example, (a - b) / (c - d) can be 3.2, 3.5, 3.8, 4, 4.3, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.3, 6.5, 6.8, 7, 7.3, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5 or 9.8, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0047] As a preferred technical solution of the present invention, in step (3), the coating agent includes a compound containing at least one of Al, Zr, W, Ti, Mg, Nb, Zn, Fe, La, B, P or F.

[0048] Preferably, the mass ratio of the metal element in the coating agent to the second modified material is (0.0001~0.003):1. For example, 0.0001:1, 0.0003:1, 0.0005:1, 0.0008:1, 0.001:1, 0.0012:1, 0.0014:1, 0.0016:1, 0.0018:1, 0.002:1, 0.0022:1, 0.0024:1, 0.0026:1, 0.0028:1 or 0.003:1, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0049] Preferably, the temperature of the third sintering is T 3 , T 3 = 250~550 °C. For example, 250 °C, 280 °C, 300 °C, 330 °C, 350 °C, 380 °C, 400 °C, 420 °C, 450 °C, 480 °C, 500 °C, 520 °C or 550 °C, etc., and the time is 6~15 h. For example, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h or 15 h, etc., but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0050] In the second aspect, the present invention provides a modified ternary material, and the modified ternary material is obtained according to the preparation method described in the first aspect.

[0051] In a third aspect, the present invention provides a battery, and the battery contains the modified ternary material described in the second aspect.

[0052] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0053] In the preparation method of the present invention, a non-cobalt metal element with a larger ionic radius is pre-oriented and doped into the shallow surface layer of the ternary material matrix to form a barrier to block the subsequent cobalt doping, which can effectively reduce the doping depth of cobalt elements and further limit more cobalt in the shallow surface layer of the particles. As a result, the cobalt concentration gradient structure has the characteristics of a high cobalt concentration in the shallow surface layer, a fast change in the cobalt concentration gradient, and a large gradient difference. In the non-shallow surface layer region, the cobalt concentration gradient changes slowly and the gradient difference is small, which is different from the relatively uniform cobalt concentration change structure manufactured by the conventional cobalt coating process. After the second sintering to dope cobalt elements into the bulk phase and form a concentration gradient structure, due to the gradient decrease of the cobalt element concentration from the outside to the inside, the proportion of cobalt elements on the material surface is high, which can improve the ionic conductivity of the material, thereby reducing the material impedance and increasing the energy density. At the same time, the cobalt concentration gradient doping structure formed by the whole particles is also beneficial to improving the cycling performance. Finally, through the third sintering for coating, the surface of the material can be repaired to obtain a modified ternary material with a complete coating layer. This coating layer can not only improve the ion transport rate, but also reduce the side reaction between the particles and the electrolyte, preventing the cobalt concentration gradient distribution from being destroyed, so as to ensure that the gradient-doped cobalt elements play their due roles. The preparation method has a simple process, is completely compatible with the existing production line mass production equipment, the production process is easy to control, and is suitable for large-scale mass production. Description of the Drawings

[0054] Figure 1 It is a test chart of the content distribution of cobalt elements in the modified ternary materials obtained in Example 1, Example 5, Example 8, Example 10 and Comparative Example 1.

[0055] Figure 2 It is a schematic cross-sectional view of the first modified material obtained in step (1) of the preparation method of Example 1.

[0056] Figure 3 It is a schematic contour comparison diagram of the cobalt concentration gradient distribution of the modified ternary materials obtained in Example 1 and Comparative Example 1. Detailed Embodiments

[0057] The technical solutions of the present invention will be further described below through specific embodiments.

[0058] Those skilled in the art should understand that the embodiments are only helpful for understanding the present invention and should not be regarded as specific limitations on the present invention.

[0059] Example 1

[0060] This embodiment provides a method for preparing a modified ternary material, and the preparation method includes:

[0061] (1) First, prepare a ternary material matrix. Mix lithium hydroxide as the lithium source and the nickel-cobalt-manganese hydroxide precursor Ni 0.75 Co 0.05 Mn 0.25 (OH) 2 evenly. The molar ratio of lithium element in the lithium source to the transition metal elements in the nickel-cobalt-manganese oxide is 1.04:1. Then, calcine at 910 °C for 12 h in an oxygen atmosphere to obtain a single-crystalline ternary material matrix Li(Ni 0.75 Co 0.05 Mn 0.25 )O 2 ;

[0062] Mix the ternary material matrix evenly with niobium pentoxide as the non-cobalt metal source with a particle size D 50 of 0.3 μm. The mass ratio of niobium element, the non-cobalt metal element in the non-cobalt metal source, to the ternary material matrix is 0.001:1. Then, conduct the first sintering at 850 °C for 8 h in an air atmosphere to form a non-cobalt metal superficial doping region from the surface to the inside of the ternary material matrix. Put the agglomerated material into a jet mill for grinding until the particle size D 50 = 3.9 μm to obtain the first modified material;

[0063] (2) Mix the obtained first modified material, cobalt hydroxide with a particle size D 50 of 0.6 μm as the cobalt source, and boric acid as the flux. The mass ratio of the flux to the cobalt source is 0.02:1, and the mass ratio of cobalt element in the cobalt source to the first modified material is 0.01:1. Then, conduct the second sintering at 800 °C for 8 h in an oxygen atmosphere to form a cobalt gradient doping region with a decreasing cobalt element concentration from the surface to the inside of the first modified material to obtain the second modified material;

[0064] (3) Mix the obtained second modified material with titanium dioxide as the coating agent. The mass ratio of titanium element, the metal element in the coating agent, to the second modified material is 0.0012:1. Conduct the third sintering at 400 °C for 10 h in an air atmosphere to obtain the modified ternary material.

[0065] Example 2

[0066] This embodiment provides a method for preparing a modified ternary material. In step (1) of the preparation method, the mass ratio of niobium element, the non-cobalt metal element in the non-cobalt metal source, to the ternary material matrix is adjusted from 0.001:1 to 0.0005:1. Except for the above, other conditions are exactly the same as those in Example 1.

[0067] Example 3

[0068] This embodiment provides a preparation method of a modified ternary material. In step (1) of the preparation method, the mass ratio of the non-cobalt metal element niobium element in the non-cobalt metal source to the ternary material matrix is adjusted from 0.001:1 to 0.002:1. Except for the above, other conditions are exactly the same as those in Example 1.

[0069] Example 4

[0070] This embodiment provides a preparation method of a modified ternary material. In step (1) of the preparation method, the mass ratio of the non-cobalt metal element niobium element in the non-cobalt metal source to the ternary material matrix is adjusted from 0.001:1 to 0.005:1. Except for the above, other conditions are exactly the same as those in Example 1.

[0071] Example 5

[0072] This embodiment provides a preparation method of a modified ternary material. In step (1) of the preparation method, the non-cobalt metal source is replaced from niobium pentoxide to tungsten trioxide. Except for the above, other conditions are exactly the same as those in Example 1.

[0073] Example 6

[0074] This embodiment provides a preparation method of a modified ternary material. In step (1) of the preparation method, the non-cobalt metal source is replaced from niobium pentoxide to molybdenum trioxide. Except for the above, other conditions are exactly the same as those in Example 1.

[0075] Example 7

[0076] This embodiment provides a preparation method of a modified ternary material. In step (2) of the preparation method, the mass ratio of the cobalt element in the cobalt source to the first modified material is adjusted from 0.01:1 to 0.005:1. Except for the above, other conditions are exactly the same as those in Example 1.

[0077] Example 8

[0078] This embodiment provides a preparation method of a modified ternary material. In step (2) of the preparation method, the mass ratio of the cobalt element in the cobalt source to the first modified material is adjusted from 0.01:1 to 0.02:1. Except for the above, other conditions are exactly the same as those in Example 1.

[0079] Example 9

[0080] This embodiment provides a preparation method of a modified ternary material. In step (2) of the preparation method, the mass ratio of the cobalt element in the cobalt source to the first modified material is adjusted from 0.01:1 to 0.03:1. Except for the above, other conditions are exactly the same as those in Example 1.

[0081] Example 10

[0082] This example provides a preparation method of modified ternary material. The temperature of the second sintering in step (2) of the preparation method is adjusted from 800 °C to 700 °C. Except for the above, other conditions are exactly the same as those in Comparative Example 1.

[0083] Example 11

[0084] This comparative example provides a preparation method of modified ternary material. The temperature of the second sintering in step (2) of the preparation method is adjusted from 800 °C to 740 °C. Except for the above, other conditions are exactly the same as those in Comparative Example 1.

[0085] Example 12

[0086] This comparative example provides a preparation method of modified ternary material. The temperature of the second sintering in step (2) of the preparation method is adjusted from 800 °C to 830 °C. Except for the above, other conditions are exactly the same as those in Comparative Example 1.

[0087] Comparative Example 1

[0088] This comparative example provides a preparation method of modified ternary material. The preparation method does not use the non-cobalt metal source to form a non-cobalt metal superficial doping region. The preparation method includes:

[0089] (1) First, prepare a ternary material matrix. Mix lithium hydroxide as the lithium source and Ni 0.75 Co 0.05 Mn 0.25 (OH) 2 uniformly. The molar ratio of lithium element in the lithium source to transition metal elements in the nickel cobalt manganese oxide is 1.04:1. Then, calcine at 910 °C for 12 h in an oxygen atmosphere. Put the agglomerated material into a jet mill for grinding until the particle size D 50 = 3.9 μm to obtain a single-crystalline ternary material matrix Li(Ni 0.75 Co 0.05 Mn 0.25 )O 2 ;

[0090] (2) Mix the obtained ternary material matrix, cobalt hydroxide as the cobalt source with a particle size D 50 of 0.6 μm, and boric acid as the flux. The mass ratio of the flux to the cobalt source is 0.02:1. The mass ratio of cobalt element in the cobalt source to the ternary material matrix is 0.01:1. Then, conduct the second sintering at 800 °C for 8 h in an oxygen atmosphere to obtain a second modified material;

[0091] (3) Mix the obtained second modified material with the coating agent titanium dioxide. The mass ratio of the metal element titanium in the coating agent to the second modified material is 0.0012:1. Then, conduct the third sintering at 400 °C for 10 h in an air atmosphere to obtain the modified ternary material.

[0092] Comparative Example 2

[0093] This comparative example provides a preparation method of a modified ternary material. During the preparation of the ternary material matrix, non-cobalt metal doping is carried out. The preparation method includes:

[0094] (1) First, prepare the ternary material matrix. Mix lithium hydroxide as the lithium source, nickel cobalt manganese hydroxide precursor Ni 0.75 Co 0.05 Mn 0.25 (OH) 2 and niobium pentoxide as the non-cobalt metal source with a particle size D 50 of 0.3 μm evenly. The molar ratio of the lithium element in the lithium source to the transition metal elements in the nickel cobalt manganese oxide is 1.04:1. The mass ratio of the non-cobalt metal element niobium in the non-cobalt metal source to the theoretically obtained ternary material matrix is 0.001:1. Then, conduct calcination at 910 °C for 12 h in an oxygen atmosphere. Put the agglomerated materials into a jet mill for pulverization until the particle size D 50 = 3.9 μm to obtain a single-crystalline ternary material matrix Li(Ni 0.75 Co 0.05 Mn 0.25 )O 2 ;

[0095] (2) Mix the obtained ternary material matrix, cobalt hydroxide with a particle size D 50 of 0.6 μm as the cobalt source, and boric acid as the flux. The mass ratio of the flux to the cobalt source is 0.02:1. The mass ratio of the cobalt element in the cobalt source to the ternary material matrix is 0.01:1. Then, conduct the second sintering at 800 °C for 8 h in an oxygen atmosphere to obtain the second modified material;

[0096] (3) Mix the obtained second modified material with the coating agent titanium dioxide. The mass ratio of the metal element titanium in the coating agent to the second modified material is 0.0012:1. Then, conduct the third sintering at 400 °C for 10 h in an air atmosphere to obtain the modified ternary material.

[0097] Characterization and testing:

[0098] Ⅰ. Test the content distribution of cobalt elements in the modified ternary materials obtained in Example 1, Example 5, Example 8, Example 10 and Comparative Example 1 by energy dispersive spectrometer (EDS), as Figure 1As shown, in all five obtained modified ternary cathode materials, there is a cobalt gradient doping region from the surface (distance from the particle center is 100%) to the center (distance from the particle center is 0%). The molar concentration (proportion) of cobalt element gradually decreases from the surface to the inside and tends to be stable. Among them, for the modified ternary materials obtained in Example 1, Example 5, Example 8 and Example 10, the cobalt concentration gradient changes rapidly and the gradient difference is large at the distance from the surface to 80% of the particle center. This region corresponds to the superficial region; as Figure 2 shown, the dotted circle represents the boundary of the superficial region inside the particle. The superficial region is the colored part between the dotted circle and the surface; after step (1), the non-cobalt metal element is only doped in the superficial region, rather than incorporated into all regions of all the bulk phases, which can then play a role in hindering subsequent cobalt doping, effectively reducing the doping depth of cobalt element, making the cobalt element more concentrated in the superficial region to form a structure with a more significant gradient. In the non-superficial region, that is, in the region between 80% of the distance from the particle center to the center, the cobalt concentration gradient changes slowly and the difference is small; as Figure 3 shown, Figure 3 the different color depths in it represent different cobalt element concentrations. The darker the color, the higher the concentration (proportion). It can be seen that in Example 1 ( Figure 3 the left figure in it), the cobalt element concentration is enriched more at the shallow surface position, and the cobalt concentration gradient tends to be stable from the shallow surface to the particle center. In contrast, in Comparative Example 1 ( Figure 3 the right figure in it), the cobalt concentration gradient is relatively uniform in the interior of the whole particle, Figure 1 showing that the slope of its curve is close to a fixed value; compared with Example 1, Example 5 and Example 8, the cobalt concentration on the surface of the material obtained in Example 10 is too high, and some cobalt additives are not effectively incorporated into the bulk phase. The cobalt element concentration distribution in other examples is shown in Table 1.

[0099]

[0100] Note: In Table 1, in the second modified material, the concentration of cobalt element on the surface is denoted as a, the concentration of cobalt element at the position 80% from the center to the surface is denoted as b, and the concentration of cobalt element at the position 50% from the center to the surface is denoted as c; the concentration of cobalt element in the ternary material matrix is denoted as d; the cobalt element concentration refers to the percentage of the amount of substance of cobalt element in the total amount of substance of nickel, cobalt and manganese elements.

[0101] Ⅱ. Electrochemical performance tests were carried out on the ternary material matrices obtained in Examples 1-12 and Comparative Example 1. The prepared nickel-cobalt-manganese ternary cathode material was tested for performance such as capacity, cycle, initial DCR, and high-temperature storage capacity retention rate on a Blue-Energy test system. The specific test method is as follows: The lithium nickel cobalt manganate ternary cathode material prepared in Example 1 was used as the cathode active material and mixed with acetylene black and PVDF as the cathode. The mass ratio of the cathode active material, acetylene black, and PVDF is 95:3:2. A lithium sheet was used as the anode, and the compaction density was 3.5 g / cm 3 , and a coin-type half-cell was assembled;

[0102] Capacity and initial DCR test steps: The charge-discharge voltage was 3.0~4.4V, the test temperature was 25°C, the charge-discharge rate was 0.2C / 0.2C, the initial DCR was tested at 100% SOC, the pulse current was 1C, and the time was 10s.

[0103] Cycle test steps: The charge-discharge voltage was 3.0~4.5V, the test temperature was 45°C, and the cycle charge-discharge rate was 1C / 1C.

[0104] Storage capacity retention rate steps: The charge-discharge voltage was 3.0~4.5V, the test temperature was 55°C, and after charging to 100% SOC, it was left stationary for 5 days.

[0105] The results are shown in Table 2.

[0106]

[0107] It can be seen from Table 2 that:

[0108] In the voltage range of 3.0~4.4V, at 25°C and 0.2C rate, compared with Comparative Example 1, the modified ternary cathode materials obtained in Examples 1-7 had obvious improvement effects in terms of initial discharge capacity and cycle retention rate, and had an obvious reduction effect in terms of initial DCR. This is because the gradient structure of the cobalt coating layer formed in Examples 1-7 is more reasonable, and while the energy density is increased, the internal resistance is also significantly decreased.

[0109] Compared with Comparative Example 2, the modified ternary cathode materials obtained in Examples 1-7 had obvious improvement effects in terms of initial discharge capacity and cycle retention rate, and had an obvious reduction effect in terms of initial DCR. This is because in Comparative Example 2, the Nb element was not doped in the shallow surface layer of the material, but was nearly evenly distributed in the bulk phase, and thus could not regulate the doping depth of the cobalt element and could not form an ideal cobalt distribution gradient structure.

[0110] Compared with Examples 2 to 5, in Example 1, with the increase in the doping amount of non-cobalt metal elements, it can be seen from Table 1 that the concentration of cobalt elements slightly increases at the surface and at the position from the center to 80% of the surface. This further reflects the regulation effect of this metal element on the doping depth of cobalt elements. In terms of the coin cell performance, the capacity shows a downward trend, and the cycle retention rate also shows a downward trend. It can be predicted that when the doping amount of non-cobalt metal elements is too large, the kinetic performance of the material will significantly decline, and when the doping amount is too small, the cycle performance will decay severely.

[0111] When comparing Example 1 with Examples 6 and 7, after replacing the non-cobalt metal element with W or Mo element, there is no obvious change in the cobalt element concentration gradient structure in Table 1, and there is also no obvious difference in the coin cell performance in Table 2. This proves that the effects of these elements are similar, and they can all play the role of regulating the cobalt element distribution gradient structure and optimizing the electrical performance.

[0112] When comparing Example 1 with Examples 8 and 9, with the change in the cobalt source coating amount, the increase in cobalt elements at the particle surface and at the position from the center to 80% of the surface is relatively obvious, but (a - b) / (c - d) is still between 3 and 10. This proves that the non-cobalt metal element can still play the role of regulating the cobalt element distribution gradient structure and does not change due to the change in the addition amount of cobalt elements.

[0113] When comparing Example 1 with Examples 10 - 12, the modified ternary cathode materials obtained in Example 1, Example 11, and Example 12 have obvious advantages in terms of the high-temperature storage capacity retention rate. This is because in the modified ternary cathode materials prepared in Example 1, Example 11, and Example 12, cobalt elements are not only retained on the surface layer but are effectively incorporated into the bulk phase of the material, which greatly reduces the electrochemical reaction activity of cobalt on the surface layer and brings many side reactions. It shows that for a specific ternary material matrix Li(Ni 0.75 Co 0.05 Mn 0.25 )O 2- , the preferred temperature range for the second sintering is 740 - 830 °C. It should be noted that for other ternary material matrices, the most suitable temperature for the second sintering may change to a certain extent, and reasonable adjustment and selection should be made.

[0114] As can be seen from the above, in the preparation method of the present invention, a non-cobalt metal element with a larger ionic radius is pre-oriented and incorporated into the shallow surface layer of the ternary material matrix to form a barrier to block the subsequent cobalt doping, which can effectively reduce the incorporation depth of cobalt elements, and then confine more cobalt to the shallow surface layer of the particles, thereby forming a structure with a relatively uniform cobalt concentration change different from that manufactured by the conventional cobalt coating process. The cobalt concentration gradient structure of this process has the characteristics of a high cobalt concentration in the shallow surface layer, a fast change in the concentration gradient, and a large difference in the concentration gradient, while the cobalt concentration gradient in the non-shallow surface area changes slowly and the gradient difference is small. After the second sintering to dope cobalt elements into the bulk phase and form a concentration gradient structure, due to the gradient decrease of the cobalt element concentration from the outside to the inside, the proportion of cobalt elements on the material surface is high, which can improve the ionic conductivity of the material, thereby reducing the material impedance and increasing the energy density; at the same time, the cobalt concentration gradient doping structure formed by the whole particles is also beneficial to improving the cycle performance. Finally, through the third sintering for coating, the surface of the material can be repaired to obtain a modified ternary material with a complete coating layer. This coating layer can not only improve the ion transport rate, but also reduce the side reaction between the particles and the electrolyte, preventing the cobalt concentration gradient distribution from being destroyed, so as to ensure that the gradient-doped cobalt elements play their due role. The preparation method has a simple process, is completely compatible with the existing production line mass production equipment, the production process is easy to control, and is suitable for large-scale mass production.

[0115] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0116] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable way. To avoid unnecessary repetition, the present invention will not describe various possible combination methods separately.

[0117] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a modified ternary material, characterized in that: The steps include: (1) mixing a ternary material matrix with a non-cobalt metal source, and performing a first sintering to form a non-cobalt metal shallow doping region from the surface of the ternary material matrix to the inside, thereby obtaining a first modified material; wherein the ion radius of the non-cobalt metal element is greater than the ion radius of the cobalt element; (2) The first modified material is mixed with a cobalt source and subjected to a second sintering to form a cobalt gradient doping region with a decreasing cobalt concentration from the surface to the inside of the first modified material, thereby obtaining a second modified material; in the second modified material, the concentration of cobalt on the surface is denoted as a, the concentration of cobalt at 80% of the distance from the center to the surface is denoted as b, and the concentration of cobalt at 50% of the distance from the center to the surface is denoted as c; the concentration of cobalt in the ternary material matrix is ​​denoted as d; then, 10>(ab) / (cd)>3; (3) The second modified material is mixed with a coating agent, and subjected to a third sintering to form a coating layer on the surface of the second modified material, thereby obtaining the modified ternary material.

2. The method for preparing the modified ternary material according to claim 1, characterized in that: In step (1), the non-cobalt metal element in the non-cobalt metal source includes at least one of W, Mo or Nb; the non-cobalt metal source includes an oxide; the particle size D of the non-cobalt metal source is 50 is 0.02-1 μm; the mass ratio of the non-cobalt metal element in the non-cobalt metal source to the ternary material matrix is ​​(0.0005-0.005):1; The ternary material matrix includes a nickel-cobalt-manganese ternary material, the chemical formula of which is Li(Ni x Co y Mn z )O2, 1>x≥0.6, 0.2≥y>0, 0.4≥z>0, and x+y+z=1.

3. The method for preparing the modified ternary material according to claim 1, characterized in that: In step (1), the temperature of the first sintering is T1, T1=700~900°C, and the time is 4~15h.

4. The method for preparing the modified ternary material according to claim 1, characterized in that: In step (1), the coverage of the non-cobalt metal superficial doping region starts from the surface of the ternary material substrate and extends to a position of 80% to 99% from the center of the ternary material substrate to the surface.

5. The method for preparing the modified ternary material according to claim 1, characterized in that: In step (2), a flux is mixed with the first modified material and the cobalt source, and then the second sintering is performed; the flux includes a compound containing at least one of Li, B, P or F; the mass ratio of the flux to the cobalt source is (0.01-0.6):1; The particle size D of the cobalt source 50 The mass ratio of the cobalt element in the cobalt source to the first modified material is (0.005-0.03):

1.

6. The method for preparing the modified ternary material according to claim 4, characterized in that: In step (2), the second sintering temperature is T2, T2=650~850°C, and the time is 4~15h.

7. The method for preparing the modified ternary material according to claim 1, characterized in that: In step (3), the coating agent includes a compound containing at least one of Al, Zr, W, Ti, Mg, Nb, Zn, Fe, La, B, P or F; The mass ratio of the metal element in the coating agent to the second modified material is (0.0001-0.003):1; The temperature of the third sintering is T3, T3=250~550°C, and the time is 6~15h.

8. A modified ternary material, characterized in that: Obtained according to the preparation method according to any one of claims 1 to 7.

9. A battery, characterized in that: The battery contains the modified ternary material according to claim 8.

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