Doped positive electrode precursor, preparation method therefor, and use thereof

Abstract

The present application provides a doped positive electrode precursor, a preparation method therefor, and a use thereof. The doped positive electrode precursor sequentially comprises, in the radial direction from the inside to the outside, an inner layer, an intermediate layer, and an outer layer. The porosity of the inner layer is greater than that of the intermediate layer, and the porosity of the intermediate layer is less than or equal to that of the outer layer. The outer layer comprises a radial channel. The doped positive electrode precursor of the present application helps improve the cycling performance and capacity of a battery.

Description

A doped cathode precursor, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202510293420.1, filed on March 12, 2025, entitled “A Doped Cathode Precursor and Its Preparation Method and Application”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of cathode precursor technology, specifically to a doped cathode precursor, its preparation method, and its application. Background Technology

[0003] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and low self-discharge rate. Among the many components of a lithium-ion battery, the performance of the cathode active material plays a crucial role in the overall battery performance. In recent years, ternary cathode materials, such as lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA), have attracted widespread attention due to their excellent electrochemical performance and high energy density. Appropriate doping elements can help improve the electrochemical performance of ternary cathode materials. For example, appropriate zirconium (Zr) doping can reduce the degree of cation mixing within the ternary cathode material, which is beneficial to Li... + Diffusion improves the migration rate and enhances the overall structural stability of ternary cathode materials, thereby improving their cycle performance. However, due to limitations in existing production processes, most doped ternary cathode materials are doped during the sintering process. This makes the doped ternary cathode materials prone to uneven distribution of dopant elements (such as Zr). Uneven distribution of dopant elements may lead to differences in electrochemical activity in local areas, thus affecting the cycle performance and capacity of the battery.

[0004] Therefore, achieving a doped cathode precursor that balances excellent cycle performance and capacity is a key research focus in this field. Summary of the Invention

[0005] This application provides a doped cathode precursor, its preparation method, and its application, which helps to improve the capacity and cycle performance of batteries and effectively solves the problems existing in existing doped cathode precursors.

[0006] This application provides a doped cathode precursor, which includes an inner layer, an intermediate layer and an outer layer in a radial direction from the inside out. The porosity of the inner layer is greater than that of the intermediate layer, the porosity of the intermediate layer is less than or equal to that of the outer layer, and the outer layer includes radial channels.

[0007] Optionally, the porosity of the inner layer is 10% to 15%, the porosity of the middle layer is 1% to 5%, and the porosity of the outer layer is 5% to 10%.

[0008] Optionally, the porosity of the doped cathode precursor is 2% to 8%; and / or, the radial dimensions of the inner layer, the intermediate layer and the outer layer are R1, R2 and R3, respectively, where R1 is 0.6 to 1.3 μm, R2 is 0.4 to 0.8 μm and R3 is 0.3 to 0.8 μm.

[0009] Optionally, the thickness of the primary particles in the inner layer is 10-50 nm, the thickness of the primary particles in the middle layer is 400-600 nm, and the thickness of the primary particles in the outer layer is 300-400 nm.

[0010] Optionally, the chemical formula of the doped cathode precursor is: (Ni a Co b Mn c M d (OH)₂, wherein 0.8 ≤ a < 1.0, 0 < b ≤ 0.1, 0 < c ≤ 0.1, a + b + c + d = 1, 0 < d ≤ 0.05, and M includes one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo; and / or, the mass percentage content of the doped element in the doped cathode precursor is 1000–8000 ppm; and / or, the tap density of the doped cathode precursor is 1.7–2.0 g / cm³. 3 ; and / or, the specific surface area of ​​the doped cathode precursor is greater than or equal to 4 m². 2 / g and less than 10m 2 / g; and / or, the D of the doped cathode precursor 50 The diameter is 3.0–4.0 μm, and the span is 0.6–1.2; and / or the length of the radial channel is 90–220 nm; and / or the sphericity of the doped cathode precursor is greater than or equal to 0.9 and less than 1.0.

[0011] This application also provides a method for preparing the doped cathode precursor as described above, comprising: introducing a raw material system including ammonia, an alkaline solution, and a metal salt solution into a bottom solution, and subjecting the reaction system to a first coprecipitation reaction at an ammonia value of A1, a pH of B1, and a flow rate of the metal salt solution of C1 to obtain a first product; and waiting for the first product to undergo a D... 50 After reaching the desired particle size, the ammonia value of the reaction system is gradually increased, the pH of the reaction system is decreased, and the flow rate of the metal salt solution is controlled at C2 to allow the reaction system to undergo a second coprecipitation reaction, yielding a second product; the D of the second product is then... 50After the desired particle size is achieved, the reaction system is subjected to a third coprecipitation reaction at an ammonia value of A3, a pH of B3, and a metal salt solution flow rate of C3 to obtain the doped cathode precursor; wherein, A1 < A3, B1 > B3, and C1 < C2 < C3.

[0012] Optionally, A1 is 2.5–3.5 g / L, A3 is 5.5–6.5 g / L; and / or, B1 is 11.60–11.80, B3 is 11.40–11.50; and / or, C1 is 1.0–2.0 L / h, C2 is 3.5–4.5 L / h, and C3 is 7.0–8.0 L / h.

[0013] Optionally, the ammonia value of the base solution is 1-4 g / L and the pH is 11.6-12.0; and / or, the temperature of the reaction system is 40-70℃; and / or, the metal salt solution comprises a mixed solution of nickel, cobalt, and manganese with a total molar concentration of 1.0-2.5 mol / L, the molar ratio of nickel, cobalt, and manganese is a:b:c, 0.8≤a<1.0, 0<b≤0.1, 0<c≤0.1, and a+b+c=1; and / or, the metal salt solution comprises a doping element, the doping element comprising one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo.

[0014] This application also provides a positive electrode active material, which is a doped positive electrode active material. The positive electrode active material includes an inner layer, an intermediate layer and an outer layer in a radial direction from the inside to the outside. The porosity of the inner layer is greater than that of the intermediate layer, the porosity of the intermediate layer is less than or equal to that of the outer layer, and the outer layer includes radial channels.

[0015] Optionally, the positive electrode active material is formed from the doped positive electrode precursor as described above or the doped positive electrode precursor prepared according to the preparation method described above.

[0016] This application also provides a positive electrode sheet, which includes the positive electrode active material as described above.

[0017] This application also provides a lithium-ion battery, which includes the positive electrode sheet as described above.

[0018] This application provides a doped cathode precursor, its preparation method, and its application. In the three-layer structure of the doped cathode precursor, the inner layer has the highest porosity and a relatively loose structure, which is conducive to the absorption and storage of lithium ions. The cathode active material can inherit the morphology of the doped cathode precursor, thus helping to alleviate the volume expansion of the cathode active material during charging and discharging. The middle layer has a lower porosity and a more compact structure, which can stabilize the structure of the doped cathode precursor and prevent particle breakage during sintering. The outer layer has a moderate porosity and a relatively compact structure, and includes radial channels to form longitudinal lithium ion channels. This helps lithium ions diffuse along the channels into the interior of the precursor during cathode sintering, increasing the amount of bound lithium salt and making the lithium salt distribution more uniform. This helps to improve the sintering uniformity of the doped cathode precursor and improve the cycle performance and capacity of the battery cathode active material, thereby effectively overcoming the problems existing in the doped cathode precursor in the prior art. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 is a cross-sectional view of the doped positive electrode precursor of Example 1;

[0021] Figure 2 is a scanning electron microscope image of the first product in Example 1;

[0022] Figure 3 is a scanning electron microscope image of the second product in Example 1;

[0023] Figure 4 is a scanning electron microscope image of the doped positive electrode precursor of Example 1 at a magnification.

[0024] Figure 5 is a scanning electron microscope image of the doped positive electrode precursor of Example 1 at another magnification;

[0025] Figure 6 is a scanning electron microscope image of the outer layer of the positive electrode precursor in Comparative Example 1;

[0026] Figure 7 is an energy spectrum mapping diagram of nickel in the doped cathode precursor of Example 1;

[0027] Figure 8 is the energy spectrum mapping diagram of cobalt in the doped cathode precursor of Example 1;

[0028] Figure 9 is an energy spectrum mapping diagram of manganese in the doped cathode precursor of Example 1;

[0029] Figure 10 is an energy spectrum mapping diagram of zirconium doping in the doped cathode precursor of Example 1;

[0030] Figure 11 is a scanning electron microscope image of the positive electrode precursor of Comparative Example 1 at a magnification;

[0031] Figure 12 is a scanning electron microscope image of the cathode precursor of Comparative Example 1 at another magnification;

[0032] Figure 13 is a scanning electron microscope image of the doped cathode precursor of Comparative Example 2 at a magnification.

[0033] Figure 14 is a scanning electron microscope image of the doped cathode precursor of Comparative Example 2 at another magnification;

[0034] Figure 15 is a scanning electron microscope image of the comparative example 4-doped cathode precursor;

[0035] Figure 16 is a cross-sectional view of the positive electrode active material of Example 1.

[0036] Explanation of reference numerals in the attached drawings: 01-inner layer, 02-middle layer, 03-outer layer, 04-radial channel, R1-radial dimension of the inner layer, R2-radial dimension of the middle layer, R3-radial dimension of the outer layer. Detailed Implementation

[0037] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0038] In existing technologies, doped cathode active materials are mostly prepared through sintering processes. These doped cathode active materials are prone to uneven distribution of doped elements, which leads to deterioration in battery cycle performance and capacity. The inventors discovered in their research that while the doped cathode precursor prepared by co-precipitation reaction has a more uniform distribution of doped elements, it suffers from significant size differences in the lithium diffusion paths, affecting sintering uniformity and adversely impacting battery performance.

[0039] To overcome the deficiencies in the prior art, this application provides a doped cathode precursor, which includes an inner layer, an intermediate layer and an outer layer in a radial direction from the inside out. The porosity of the inner layer is greater than that of the intermediate layer, the porosity of the intermediate layer is less than or equal to that of the outer layer, and the outer layer includes radial channels.

[0040] Figure 1 is a cross-sectional view of the doped cathode precursor according to an embodiment of this application. To better understand the distribution of the inner, intermediate, and outer layers in the doped cathode precursor, Figure 1 is used as an example for explanation below. As shown in Figure 1, the doped cathode precursor includes an inner layer (01), an intermediate layer (02), and an outer layer (03) in the radial direction from the inside to the outside. The inner layer (01) is located inside the doped cathode precursor, the intermediate layer (02) surrounds the outer side of the inner layer (01), and the outer layer (03) surrounds the outer side of the intermediate layer (02). More specifically, the doped cathode precursor can be assumed to be a sphere, the inner layer (01) is a small sphere located inside the sphere, the intermediate layer (02) is an annular region surrounding the outer side of the small sphere, and the outer layer (03) is an annular region surrounding the outer side of the intermediate layer (02).

[0041] It is understood that the doped cathode precursor in the embodiments of this application is a secondary particle formed by the agglomeration of primary particles, which has a porous structure. In the three-layer structure of the doped cathode precursor, the inner layer (01) has the highest porosity and a relatively loose structure, which is conducive to the absorption and storage of lithium ions and alleviates the volume expansion of the cathode active material during charging and discharging. The middle layer (02) has a lower porosity and a relatively dense structure, which can stabilize the structure of the doped cathode precursor and prevent particle breakage during sintering. The outer layer (03) has a moderate porosity and a relatively dense structure. The outer layer (03) includes a radial channel (04), which is a hollow channel distributed radially. This radial channel forms a longitudinal lithium ion channel, which helps lithium ions diffuse into the precursor interior along the channel during cathode sintering, increasing the amount of bound lithium salt. The lithium salt distribution is more uniform, which helps improve the sintering uniformity of the doped cathode precursor and improves the cycle performance and capacity of the battery cathode active material, thereby effectively overcoming the problems existing in the doped cathode precursor in the prior art.

[0042] Therefore, the doped cathode precursor of this application embodiment can have both good cycle performance and capacity, effectively overcoming the problems existing in the doped ternary cathode active materials in the prior art.

[0043] In some embodiments, the porosity of the inner layer is 10%–15%, the porosity of the middle layer is 1%–5%, and the porosity of the outer layer is 5%–10%. By further controlling the porosity of the inner, middle, and outer layers within the aforementioned ranges, it helps to better improve the structural stability of the doped cathode precursor and the absorption and storage performance of lithium ions, and further helps to improve the cycle performance and capacity of the positive electrode active material of lithium-ion batteries, thereby effectively solving the problems existing in doped cathode precursors. Exemplarily, the porosity of the inner layer can be a range of 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof; the porosity of the middle layer can be a range of 1%, 2%, 3%, 4%, 5%, or any combination thereof; and the porosity of the outer layer can be a range of 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof.

[0044] In some embodiments, the thickness of the primary particles in the inner layer is 10-50 nm, the thickness of the primary particles in the middle layer is 400-600 nm, and the thickness of the primary particles in the outer layer is 300-400 nm. The inner layer has thinner primary particles that interweave with each other, leaving many gaps, resulting in a loose and porous honeycomb structure. This facilitates the absorption and storage of lithium ions and mitigates the volume expansion of the positive electrode active material during charging and discharging. The middle layer has thicker primary particles that are staggered and tightly packed with no obvious gaps. This dense structure helps stabilize the structure of the doped positive electrode precursor and prevents particle breakage during sintering. The outer layer has a moderate thickness of primary particles and a relatively dense structure. The primary particles are oriented to form radially distributed hollow channels, which in turn form longitudinal lithium ion channels. This allows lithium ions to diffuse along these channels into the precursor during positive electrode sintering, increasing the amount of bound lithium salt and resulting in a more uniform distribution of lithium salt. This improves the sintering uniformity of the doped positive electrode precursor and enhances the cycle performance and capacity of the battery's positive electrode active material, effectively overcoming the problems existing in current doped positive electrode precursor technologies.

[0045] Furthermore, the primary particles in the inner layer may include 2 to 10 nanosheets, i.e., they are formed by stacking 2 to 10 nanosheets; the primary particles in the middle layer may include 80 to 120 nanosheets, i.e., they are formed by stacking 80 to 120 nanosheets; and the primary particles in the outer layer may include 60 to 80 nanosheets, i.e., they are formed by stacking 60 to 80 nanosheets. The inner layer has fewer nanosheet layers of primary particles, which are interwoven and have many gaps, resulting in a loose and porous honeycomb structure. This structure is beneficial for lithium-ion absorption and storage, and mitigates the volume expansion of the positive electrode active material during charging and discharging. The middle layer has more nanosheet layers of primary particles, which are interleaved and tightly packed with no obvious gaps. This dense structure helps stabilize the structure of the doped positive electrode precursor and prevents particle breakage during sintering. The outer layer has a moderate number of nanosheet layers of primary particles, resulting in a relatively dense structure. The primary particles are oriented to form radially distributed hollow channels, which in turn form longitudinal lithium-ion channels. This facilitates the diffusion of lithium ions into the precursor during positive electrode sintering, increasing the amount of bound lithium salt and resulting in a more uniform distribution of lithium salt. This improves the sintering uniformity of the doped positive electrode precursor and enhances the cycle performance and capacity of the battery positive electrode active material, effectively overcoming the problems existing in doped positive electrode precursors in the prior art.

[0046] In some embodiments, the porosity of the doped cathode precursor decreases first and then increases from the inside out. The inner layer has higher porosity, fewer nanosheets (layers), and thinner primary particles. The primary particles intertwine to form a loose and porous honeycomb structure, which is beneficial for the absorption and storage of lithium ions and alleviates volume expansion during charging and discharging. The middle layer has lower porosity, more nanosheets (layers), and thicker primary particles. The main function of the middle layer is to stabilize the structure and prevent particle breakage during sintering. The outer layer is relatively dense, with a moderate number of nanosheets (layers) and a moderate thickness of primary particles. The primary particles are oriented to form radially distributed hollow channels, i.e., radial channels, and also form longitudinal lithium ion channels. During cathode sintering, lithium ions can diffuse along the channels into the interior of the precursor, and the number of bound lithium salts is greater and the distribution is more uniform, which significantly improves the cycle performance and capacity of the positive electrode active material of lithium-ion batteries.

[0047] In some embodiments, the radial channels in the outer layer, i.e. the lithium-ion channels, can be 90 to 220 nm in length. This helps lithium ions diffuse along the channels into the precursor during cathode sintering, increasing the amount of bound lithium salt and making the lithium salt distribution more uniform. This helps improve the sintering uniformity of the doped cathode precursor and improves the cycle performance and capacity of the battery cathode active material, thereby effectively overcoming the problems existing in the doped cathode precursor in the prior art.

[0048] In some embodiments, the porosity of the doped cathode precursor is 2% to 8%. Since the cathode active material can inherit the morphology of the doped cathode precursor, it helps to improve the cycle performance and capacity of the cathode active material. Exemplarily, the porosity of the doped cathode precursor can be a range of 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any combination thereof.

[0049] The radial dimensions of the inner layer, intermediate layer, and outer layer are R1, R2, and R3, respectively. Taking Figure 1 as an example, it can be seen that the radial dimension R1 of the inner layer is its diameter, the radial dimension R2 of the intermediate layer is its width, and the radial dimension R3 of the outer layer is its width. Specifically, R1 can be 0.6–1.3 μm, for example, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.3 μm, or any combination thereof; R2 can be 0.4–0.8 μm, for example, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or any combination thereof; and R3 can be 0.3–0.8 μm, for example, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or any combination thereof. By controlling the radial dimensions of the inner, middle, and outer layers to meet the above range, it is helpful to improve the structural stability of the doped cathode precursor and the absorption and storage performance of lithium ions, and further help to improve the cycle performance and capacity of the cathode active material of lithium-ion batteries, thereby effectively solving the problems existing in the doped cathode precursor.

[0050] The doping element in the doped cathode precursor of this application may include one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo. Zr is preferred among the above doping elements. After Zr is incorporated into the doped cathode precursor via bulk doping, it can reduce the surface energy of the primary particles, alleviate crystal nucleus agglomeration, improve sphericity, and reduce the particle size distribution width (SPAN). Simultaneously, Zr... 4+ The ionic radius of Zr is slightly larger than that of nickel, cobalt, and manganese, and it is incorporated into the unit cell. 4+ This increases the interlayer spacing of the crystal layers and expands the lithium-ion transport channels, thereby helping to improve the cycle performance and capacity of the battery.

[0051] In some embodiments, the sphericity of the doped cathode precursor is greater than or equal to 0.9 and less than 1.0. In some embodiments, the dopant element in the doped cathode precursor is uniformly distributed from the inside to the outside, which helps to improve the cycle performance and capacity of the battery. In some embodiments, the mass percentage of the dopant element in the doped cathode precursor is 1000 to 8000 ppm, which helps to improve the cycle performance and capacity of the battery.

[0052] Furthermore, the chemical formula of the aforementioned doped cathode precursor can be: (Nia Co b Mn c M d (OH)₂, wherein 0.8 ≤ a < 1.0, 0 < b ≤ 0.1, 0 < c ≤ 0.1, a + b + c + d = 1, 0 < d ≤ 0.05, and M includes one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo. That is, M is a dopant element.

[0053] The tap density of the above-mentioned doped cathode precursor can be 1.7–2.0 g / cm³. 3 This helps improve battery capacity.

[0054] The specific surface area of ​​the above-mentioned doped cathode precursor can be greater than or equal to 4 m². 2 / g and less than 10m 2 / g. The smaller specific surface area of ​​this doped cathode precursor helps reduce side reactions and improve cycle performance.

[0055] The above-mentioned doped cathode precursor D 50 It can be 3.0 to 4.0 μm, and is suitable for sintering single-crystal positive electrode active materials.

[0056] Doped cathode precursors are prone to exhibiting a wide particle size distribution. Taking zirconium doping as an example, compared to nickel-cobalt-manganese hydroxides, the solubility product (Ksp) of Zr(OH)4 is too low, only 6.30*10. -49 This makes Zr(OH)4 more likely to precipitate and nucleate individually in the cathode precursor doping reaction system, producing small particles, thus resulting in an excessively wide particle size distribution of the zirconium-doped cathode precursor. The SPAN of the doped cathode precursor in this application embodiment is relatively narrow, ranging from 0.6 to 1.2, which helps improve the uniformity of the lithium diffusion path, enhances sintering uniformity, and contributes to improving the cycle performance and capacity of the battery. In this application embodiment, the above-mentioned SPAN is equal to (D 90 -D 10 ) / D 50 .

[0057] Most existing doping technologies involve doping during the cathode sintering process. However, due to the atomic size of the dopant elements (e.g., the relatively large size of zirconium atoms), it is difficult for the dopant elements to penetrate into the cathode active material during sintering. This results in uneven distribution of the dopant elements inside and outside the cathode active material, and the doping amount cannot be controlled, making atomic-level doping difficult to achieve. Furthermore, the low solubility product (Ksp) of the aforementioned dopant elements (e.g., zirconium) leads to their easier precipitation and individual nucleation in the cathode precursor doping reaction system, producing small particles. This results in an excessively wide particle size distribution in the doped cathode precursor, failing to meet the capacity and cycle requirements of the cathode active material. It also leads to irregular morphology and poor sphericity in the doped cathode precursor. During the sintering process of preparing cathode active materials (e.g., single-crystal cathode active materials) using these doped precursors, the size differences in the lithium diffusion path are significant, resulting in poor sintering uniformity and negatively impacting battery performance.

[0058] Based on this, this application also provides a method for preparing the above-mentioned doped cathode precursor, comprising: introducing a raw material system including ammonia, an alkaline solution, and a metal salt solution into a bottom liquid, and carrying out a first coprecipitation reaction in the reaction system at an ammonia value of A1, a pH of B1, and a flow rate of the metal salt solution of C1 to obtain a first product; waiting for the first product to undergo a D... 50 After reaching the desired particle size, the ammonia value of the reaction system is gradually increased, the pH of the reaction system is decreased, and the flow rate of the metal salt solution is controlled at C2 to allow the reaction system to undergo a second coprecipitation reaction, yielding the second product; wait for the D of the second product... 50 After the desired particle size is achieved, the reaction system is subjected to a third coprecipitation reaction at an ammonia value of A3, a pH of B3, and a metal salt solution flow rate of C3 to obtain a doped cathode precursor; wherein, A1 < A3, B1 > B3, and C1 < C2 < C3.

[0059] The above preparation method can be divided into three stages: the first stage, the second stage, and the third stage. The first stage is the first coprecipitation reaction process, the second stage is the second coprecipitation reaction process, and the third stage is the third coprecipitation reaction process. In the first stage, the reaction system undergoes the first coprecipitation reaction under conditions of low ammonia value (low ammonia), high pH, ​​and low metal salt solution flow rate. At this time, the supersaturation of ions (including dopant ions) in the reaction system is high, and the dopant ions mainly undergo precipitation reactions, resulting in the formation of a certain number of crystal nuclei in the reaction system at a high nucleation rate. This helps to form primary particles with fewer lamellar layers and loose packing, thus forming a loosely structured inner layer (the first product). In the second stage, the reaction system undergoes the second coprecipitation reaction under conditions of moderate metal salt solution flow rate, gradually increasing ammonia value, and gradually decreasing pH. During the second coprecipitation reaction, the ammonia value and pH of the reaction system dynamically change, the growth rate gradually increases, and the nucleation rate gradually decreases. This helps to form an intermediate layer with increased number of primary particle lamellar layers and dense packing, thus obtaining a second product including both an inner layer and an intermediate layer. It is important to note that during the second coprecipitation reaction described above, both the ammonia value (ammonia concentration) and pH are dynamically changing. The ammonia value gradually increases (gradient increase), for example, from A1 to A3, while the pH gradually decreases (gradient decrease), for example, from B1 to B3, while the metal salt flow rate remains constant at C2. In the third stage, the reaction system undergoes a third coprecipitation reaction under conditions of high metal salt solution flow rate, high ammonia value (high ammonia), and low pH. The growth rate further increases, the nucleation rate further decreases, and the particles undergo directional adhesion and ripening, thereby forming a hollow radial channel (radial lithium-ion channel) formed by the directional arrangement of the particles, and a relatively dense outer layer, resulting in a doped cathode precursor consisting of an inner layer, a middle layer, and an outer layer.

[0060] Since the complexation reaction and precipitation reaction are in competition, in the second and third stages, the ammonia value is increased, and under conditions such as gradually increasing ammonia value, more dopant ions (such as Zr) are present in the reaction system. 4+ It can complex with ammonia, causing the dopant ions to mainly undergo complexation reactions in the reaction system. The supersaturation of the dopant ions in the reaction system is low, and a small amount of free dopant ions preferentially co-precipitate with nickel, cobalt, and manganese on the precursor surface, rather than reacting with OH- in the system. - The reaction is carried out in a way that prevents the formation of fine powder through nucleation, thus effectively solving the problem of small particles and wide spans in the synthesis of doped cathode precursors.

[0061] The above preparation method dynamically adjusts the flow rate of the metal salt solution, the ammonia value (the amount of ammonia water introduced), and the pH (the amount of alkaline solution introduced) during the reaction process. It employs a process that includes operations such as low ammonia value in the early stage, high ammonia value in the later stage, high pH in the early stage, low pH in the later stage, low metal salt flow rate in the early stage, and high metal salt flow rate in the later stage. This process prepares a doped cathode precursor with three different layered structures: an inner layer, a middle layer, and an outer layer. This helps to improve the cycle performance and capacity of the battery. In addition, the SPAN and doping content of this doped precursor are controllable, with regular morphology, high sphericity, and relatively uniform distribution of doped elements, overcoming the shortcomings of the prior art.

[0062] The preparation method is simple to operate and suitable for industrial application.

[0063] This application does not limit the reaction site for the above preparation method; for example, it can be carried out in a reaction vessel (e.g., a 100L reaction vessel). In specific implementation, an inert gas, such as high-purity nitrogen, can be introduced below the liquid surface of the reaction system to ensure that the reaction system is in an inert atmosphere and to prevent oxidation reactions. The flow rate of the inert gas (e.g., nitrogen) can be 0.1-1.0 m³ / s. 3 / h. The ammonia value of the above-mentioned base solution can be 1-4 g / L, and the pH can be 11.6-12.0.

[0064] The base solution can be prepared by the following process: Under stirring at 300-900 rpm, ammonia water is added to water (such as deionized water) and the ammonia value is controlled at 1-4 g / L. Then, an alkaline solution is passed into it and the pH is adjusted to 11.6-12.0 to obtain the base solution.

[0065] In some embodiments, the ammonia value A1 in the first stage is 2.5 to 3.5 g / L, the ammonia value A3 in the third stage is 5.5 to 6.5 g / L, and the ammonia value in the second stage gradually increases from A1 to A3, which helps to further control the porosity of the inner, middle and outer layers within a suitable range, thereby further improving the cycle performance and capacity of the battery.

[0066] In some embodiments, the pH value B1 in the first stage is 11.60 to 11.80, the pH value B3 in the third stage is 11.40 to 11.50, and the pH value in the second stage gradually decreases from B1 to B3, which helps to further control the porosity of the inner, middle and outer layers within a suitable range, thereby further improving the cycle performance and capacity of the battery.

[0067] In this embodiment, doping is performed during the synthesis of the doped cathode precursor. Specifically, the doping amount can be precisely controlled by adjusting the flow rate of the metal salt solution (feed flow rate), thus achieving atomic-level doping.

[0068] In some embodiments, the flow rate C1 of the metal salt solution in the first stage is 1.0–2.0 L / h, the flow rate C2 of the metal salt solution in the second stage is 3.5–4.5 L / h, and the flow rate C3 of the metal salt solution in the third stage is 7.0–8.0 L / h. This helps to further control the porosity of the inner, middle, and outer layers within a suitable range, thereby further improving the cycle performance and capacity of the battery. It is understood that the aforementioned metal salt solution also includes doping elements, which may include one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo, preferably Zr. The concentration of the doping element in the metal salt solution can be 0.05–2.5 mol / L. For example, the aforementioned metal salt solution may include a mixed solution of nickel, cobalt, and manganese with a total molar concentration of 0.05 to 2.5 mol / L, such as 0.05, 0.1, 1.0, 2, 2.5 mol / L or any combination thereof, wherein the molar ratio of nickel, cobalt, and manganese is a:b:c, 0.8≤a<1.0, 0<b≤0.1, 0<c≤0.1, and a+b+c=1.

[0069] In practice, a nickel source, a cobalt source, a manganese source, a dopant, and water (such as deionized water) can be mixed to prepare the aforementioned metal salt solution. The nickel source may include nickel sulfate, the cobalt source may include cobalt sulfate, the manganese source may include manganese sulfate, and the dopant may include zirconium sulfate (such as anhydrous zirconium sulfate).

[0070] The ammonia solution described above acts as a complexing agent, and its concentration can be 5–12 mol / L. Specifically, it can be prepared by mixing ammonia solution with an ammonia content of 25% by mass with water. The alkaline solution described above may include an aqueous solution of sodium hydroxide, with a concentration of 5–12 mol / L.

[0071] In practice, during the first coprecipitation reaction, the thickener can be turned on after the reaction liquid of the reaction system has overflowed for a period of time (e.g., 4 hours) to increase its solid content.

[0072] In the third coprecipitation reaction, the reaction can be terminated after the particle size of the doped cathode precursor reaches 3.0–4.0 μm to obtain the doped cathode precursor, which can be used for the sintering preparation of single-crystal cathode active materials. After the third coprecipitation reaction, the resulting mixed slurry can be aged, centrifuged, washed, dried, sieved, and iron removed to obtain the doped cathode precursor (e.g., zirconium-doped nickel-cobalt-manganese precursor). Specifically, the aging process can be carried out in an aging kettle, the centrifugation washing can be carried out in a centrifuge, and the drying can be carried out in a forced-air drying oven. During the centrifugation washing process, a hot alkaline solution (e.g., 10 mol / L concentration) or hot water can be used as the washing liquid, and the washing time is 20–40 min. The temperature of the hot alkaline solution or hot water can be 50–70 °C, and the hot alkaline solution can include at least one of sodium hydroxide and potassium hydroxide. During the drying process, the temperature can be 110–130 °C, and the drying time can be 15–20 h. In practice, a 325-mesh sieve can be used for sieving.

[0073] In some embodiments, the expected particle size (D) of the first product 50 The particle size can be 0.6–1.3 μm, and the expected particle size of the second product (D) is... 50 The particle size can be 1.0–2.2 μm, and the expected particle size (D) of the doped cathode precursor is... 50 The size can be 3.0 to 4.0 μm.

[0074] In practical applications, the temperature of the above reaction system can be 40–70℃.

[0075] Based on the same inventive concept, this application also provides a positive electrode active material, which is a doped positive electrode active material. From the inside out in the radial direction, the positive electrode active material sequentially includes an inner layer, a middle layer, and an outer layer. The porosity of the inner layer is greater than that of the middle layer, the porosity of the middle layer is less than or equal to that of the outer layer, and the outer layer includes radial channels. Based on the foregoing description, this positive electrode active material helps improve the cycle performance and capacity of the battery, which will not be elaborated further here.

[0076] The positive electrode active material is formed from the doped positive electrode precursor described above or from a doped positive electrode precursor prepared according to the above method. Based on this doped positive electrode precursor, the positive electrode active material helps to improve the cycle performance and capacity of the battery, which will not be elaborated here.

[0077] In some embodiments, the above-mentioned positive electrode active material is obtained by sintering a mixture of the above-mentioned doped positive electrode precursor and a lithium salt. Specifically, the above-mentioned lithium salt may include at least one of lithium carbonate and lithium hydroxide.

[0078] Based on the same inventive concept, this application also provides a positive electrode sheet, which includes the above-mentioned positive electrode active material.

[0079] The positive electrode sheet in this application specifically includes a positive current collector and a positive active layer formed of the above-mentioned positive active material disposed on the surface of the positive current collector.

[0080] In the specific preparation of the positive electrode sheet, for example, the above-mentioned positive electrode active material of this application can be dispersed with a conductive agent and a binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained. For example, the positive electrode active layer includes 70-99 wt% positive electrode active material, 0.5-15 wt% conductive agent, and 0.5-15 wt% binder by mass percentage, and further includes 80-98 wt% positive electrode active material, 1-10 wt% conductive agent, and 1-10 wt% binder.

[0081] The material of the positive current collector can be at least one of aluminum foil and nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0082] The battery prepared using this positive electrode has high capacity and excellent cycle performance.

[0083] Based on the same inventive concept, this application provides a lithium-ion battery, which includes the above-described positive electrode.

[0084] It is conceivable that the lithium-ion battery in this application embodiment, in addition to the aforementioned positive electrode sheet, also includes a negative electrode sheet, an electrolyte, and a separator. This application embodiment does not strictly limit the negative electrode active material in the negative electrode sheet; it can be at least one of the negative electrode active materials commonly used in lithium-ion batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), and tin-based negative electrode materials (mainly including tin and tin alloys). The embodiments of this application do not strictly limit the selection of electrolyte, and may include one or more of the solvents commonly used in lithium-ion battery electrolytes, as well as the electrolyte lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). This application does not strictly limit the choice of separator material; it can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene (PP), polyethylene (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven membrane, or separator with ceramic coating. In the preparation of a lithium-ion battery, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete the preparation of the lithium-ion battery.

[0085] This lithium-ion battery has high capacity and excellent cycle performance.

[0086] The present application will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0087] Example 1

[0088] This embodiment provides a method for preparing a doped cathode precursor, including:

[0089] Nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate, and deionized water were mixed to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn=88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; an ammonia solution with a concentration of 9.8 mol / L and a sodium hydroxide solution with a concentration of 11 mol / L were also prepared.

[0090] While stirring at 600 rpm, the above-mentioned ammonia solution was added to deionized water at 60°C, controlling the ammonia concentration to 3.0 g / L. Then, an 11 mol / L sodium hydroxide aqueous solution was passed into the solution to adjust the pH to 11.6–11.80. High-purity nitrogen gas was then introduced below the liquid surface at a flow rate of 0.3 m³ / h. 3 / h, to obtain the base liquid;

[0091] A raw material system comprising the above-mentioned ammonia water, the above-mentioned sodium hydroxide aqueous solution, and the metal salt solution is introduced into the bottom liquid. The reaction system is subjected to a first coprecipitation reaction at an ammonia value A1 of 3.0 g / L, a pH value B1 of 11.6 to 11.80, and a flow rate of the metal salt solution C1 of 1.5 L / h to obtain the first product.

[0092] D of the first product 50 After reaching 1.2 μm, the ammonia value of the reaction system was gradually increased to 6.0 g / L, and the pH of the reaction system was gradually decreased to 11.40-11.50. The flow rate C2 of the metal salt solution was controlled at 4.0 L / h to allow the reaction system to undergo a second coprecipitation reaction and obtain the second product.

[0093] The second product D 50 After reaching 2.2 μm, the reaction system was subjected to a third coprecipitation reaction at an ammonia value of 6.0 g / L, a pH value of 11.40–11.50, and a metal salt solution flow rate of 7.5 L / h. The third coprecipitation reaction was stopped when the product particle size reached 3.8 μm.

[0094] Then, after aging the reaction solution of the third coprecipitation, it was first centrifuged and washed for 20 min with a 10 mol / L hot alkaline solution, then centrifuged and washed for 40 min with hot water, then dried at 130℃ for 20 h, and then sieved through a 325 mesh sieve to remove iron, thus obtaining the doped positive electrode precursor of this embodiment.

[0095] Example 2

[0096] This embodiment is basically the same as Embodiment 1, except that:

[0097] The concentration of Zr in the metal salt solution was 0.1 mol / L; other conditions remained unchanged.

[0098] Example 3

[0099] This embodiment is basically the same as Embodiment 1, except that:

[0100] The concentration of Zr in the metal salt solution was 0.15 mol / L; other conditions remained unchanged.

[0101] Example 4

[0102] This embodiment is basically the same as Embodiment 1, except that:

[0103] The concentration of Zr in the metal salt solution was 0.25 mol / L; other conditions remained unchanged.

[0104] Example 5

[0105] This embodiment is basically the same as Example 1, except that: the ammonia value of the base solution is 2.5 g / L and the pH is 11.60; in the first coprecipitation reaction, A1 is 2.5 g / L, B1 is 11.60, and C1 is 1.0 L / h; in the second coprecipitation reaction, the ammonia value of the reaction system is gradually increased to 5.5 g / L, and the pH of the reaction system is gradually decreased to 11.40, with C2 at 3.5 L / h; in the third coprecipitation reaction, A3 is 5.5 g / L, B3 is 11.40, and C3 is 7.0 L / h; the reaction temperature is 40℃; and other conditions remain unchanged.

[0106] Example 6

[0107] This embodiment is basically the same as Example 1, except that: the ammonia value of the base solution is 3.5 g / L and the pH is 11.80; in the first coprecipitation reaction, A1 is 3.5 g / L, B1 is 11.80, and C1 is 2.0 L / h; in the second coprecipitation reaction, the ammonia value of the reaction system is gradually increased to 6.5 g / L, and the pH of the reaction system is gradually decreased to 11.50, with C2 at 4.5 L / h; in the third coprecipitation reaction, A3 is 6.5 g / L, B3 is 11.50, and C3 is 8.0 L / h; the reaction temperature is 70℃; and other conditions remain unchanged.

[0108] Example 7

[0109] This embodiment is basically the same as Example 1, except that: the ammonia value of the base solution is 3.0 g / L and the pH is 11.70; in the first coprecipitation reaction, A1 is 3.0 g / L, B1 is 11.70, and C1 is 1.5 L / h; in the second coprecipitation reaction, the ammonia value of the reaction system is gradually increased to 6.0 g / L, and the pH of the reaction system is gradually decreased to 11.45, with C2 at 4.5 L / h; in the third coprecipitation reaction, A3 is 6.0 g / L, B3 is 11.45, and C3 is 7.5 L / h; other conditions remain unchanged.

[0110] Example 8

[0111] This embodiment is basically the same as Example 1, except that: the ammonia value of the base solution is 1.0 g / L and the pH is 11.70; in the first coprecipitation reaction, A1 is 1.0 g / L, B1 is 11.70, and C1 is 1.5 L / h; in the second coprecipitation reaction, the ammonia value of the reaction system is gradually increased to 6.0 g / L, and the pH of the reaction system is gradually decreased to 11.45, with C2 at 4.5 L / h; in the third coprecipitation reaction, A3 is 6.0 g / L, B3 is 11.45, and C3 is 7.5 L / h; other conditions remain unchanged.

[0112] Example 9

[0113] This embodiment is basically the same as Embodiment 1, except that: the D of the first product to be produced... 50 After reaching 0.6 μm, a second precipitation reaction is carried out; wait for the D of the second product to reach a certain concentration. 50 After reaching 2.2 μm, the third precipitation reaction is carried out; wait for the D of the product of the third precipitation reaction to be determined. 50 Once the precipitate reaches 3.8 μm, the third precipitation reaction is stopped; other conditions remain unchanged.

[0114] Example 10

[0115] This embodiment is basically the same as Embodiment 1, except that: the D of the first product to be produced... 50 After reaching 1.5 μm, a second precipitation reaction is carried out; wait for the D of the second product to reach a certain concentration. 50 After reaching 2.1 μm, the third precipitation reaction is carried out; wait for the D of the product of the third precipitation reaction to be determined. 50 Once the precipitate reaches 2.9 μm, the third precipitation reaction is stopped; other conditions remain unchanged.

[0116] Example 11

[0117] This embodiment is basically the same as Embodiment 1, except that: the D of the first product to be produced... 50 After reaching 0.4 μm, a second precipitation reaction is carried out; wait for the D of the second product to reach a certain concentration. 50 After reaching 2.4 μm, the third precipitation reaction is carried out; wait for the D of the product of the third precipitation reaction to be determined. 50 Once the precipitate reaches 2.8 μm, the third precipitation reaction is stopped; other conditions remain unchanged.

[0118] Example 12

[0119] This embodiment is basically the same as Example 1, except that lanthanum chloride hexahydrate is used instead of anhydrous zirconium sulfate, while other conditions remain unchanged.

[0120] Comparative Example 1

[0121] This comparative example is basically the same as Example 1, except that: the metal salt solution does not contain zirconium sulfate, that is, the positive electrode precursor of Comparative Example 1 is not doped; other conditions remain unchanged.

[0122] Comparative Example 2

[0123] This comparative example provides a method for preparing a doped cathode precursor, including:

[0124] Nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate, and deionized water were mixed to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn=88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; an ammonia solution with a concentration of 9.8 mol / L and a sodium hydroxide solution with a concentration of 11 mol / L were also prepared.

[0125] While stirring at 600 rpm, the above-mentioned ammonia solution was added to deionized water, controlling the ammonia concentration to 3.0 g / L. Then, an 11 mol / L sodium hydroxide aqueous solution was passed into the solution to adjust the pH to 11.6–11.80. High-purity nitrogen gas was then introduced below the liquid surface at a flow rate of 0.3 m³ / h. 3 / h, to obtain the base liquid;

[0126] A raw material system comprising the above-mentioned ammonia water, the above-mentioned sodium hydroxide aqueous solution, and the metal salt solution is introduced into the bottom liquid. The reaction system is subjected to a first coprecipitation reaction at an ammonia value A1 of 3.0 g / L, a pH value B1 of 11.6 to 11.80, and a flow rate of the metal salt solution C1 of 1.5 L / h to obtain the first product.

[0127] After the particle size of the first product reaches 3.5 μm, the first coprecipitation reaction is stopped. Then, the reaction solution of the first coprecipitation is aged, centrifuged and washed with 10 mol / L hot alkaline solution for 20 min, then centrifuged and washed with hot water for 40 min, then dried at 130℃ for 20 h, and then sieved through a 325 mesh sieve to remove iron, thus obtaining the doped cathode precursor of this comparative example.

[0128] In other words, Comparative Example 2 only underwent the first coprecipitation reaction, while other conditions remained unchanged from Example 1.

[0129] Comparative Example 3

[0130] This comparative example provides a method for preparing a doped cathode precursor, including:

[0131] Nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate, and deionized water were mixed to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn=88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; an ammonia solution with a concentration of 9.8 mol / L and a sodium hydroxide solution with a concentration of 11 mol / L were also prepared.

[0132] While stirring at 600 rpm, the above-mentioned ammonia solution was added to deionized water, controlling the ammonia concentration to 3.0 g / L. Then, an 11 mol / L sodium hydroxide aqueous solution was passed into the solution to adjust the pH to 11.6–11.80. High-purity nitrogen gas was then introduced below the liquid surface at a flow rate of 0.3 m³ / h. 3 / h, to obtain the base liquid;

[0133] A raw material system comprising the above-mentioned ammonia water, the above-mentioned sodium hydroxide aqueous solution, and the metal salt solution is introduced into the bottom liquid. The ammonia value of the reaction system is gradually increased to 6.0 g / L, and the pH of the reaction system is gradually decreased to 11.40-11.50. The flow rate of the metal salt solution is controlled at 4.0 L / h, so that the reaction system undergoes a second coprecipitation reaction to obtain the second product.

[0134] The second product D 50 Once the precipitate reaches 3.5 μm, the second coprecipitation reaction is stopped.

[0135] The reaction solution of the second coprecipitate was then aged, centrifuged and washed for 20 min with a 10 mol / L hot alkaline solution, then centrifuged and washed for 40 min with hot water, dried at 130℃ for 20 h, and then sieved through a 325 mesh sieve to remove iron, thus obtaining the doped cathode precursor of this comparative example.

[0136] In other words, Comparative Example 3 only underwent the second coprecipitation reaction, while other conditions remained unchanged from Example 1.

[0137] Comparative Example 4

[0138] This comparative example provides a method for preparing a doped cathode precursor, including:

[0139] Nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate, and deionized water were mixed to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn=88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; an ammonia solution with a concentration of 9.8 mol / L and a sodium hydroxide solution with a concentration of 11 mol / L were also prepared.

[0140] While stirring at 600 rpm, the above-mentioned ammonia solution was added to deionized water, controlling the ammonia concentration to 3.0 g / L. Then, an 11 mol / L sodium hydroxide aqueous solution was passed into the solution to adjust the pH to 11.6–11.80. High-purity nitrogen gas was then introduced below the liquid surface at a flow rate of 0.3 m³ / h. 3 / h, to obtain the base liquid;

[0141] A raw material system comprising the above-mentioned ammonia water, the above-mentioned sodium hydroxide aqueous solution, and the metal salt solution is introduced into the bottom liquid, and the reaction system is subjected to a third coprecipitation reaction at an ammonia value A3 of 6.0 g / L, a pH value B3 of 11.40 to 11.50, and a metal salt solution flow rate C3 of 7.5 L / h.

[0142] Then, after aging, the reaction solution of the third coprecipitate was first washed by centrifugation with a 10 mol / L hot alkaline solution for 20 min, then washed by centrifugation with hot water for 40 min, then dried at 130℃ for 20 h, and then sieved through a 325 mesh sieve to remove iron, thus obtaining the doped cathode precursor of this comparative example.

[0143] In other words, Comparative Example 4 only underwent the third coprecipitation reaction, while other conditions remained unchanged from Example 1.

[0144] Comparative Example 5

[0145] This comparative example provides a method for preparing a doped cathode precursor, including:

[0146] Nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate, and deionized water were mixed to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn=88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; an ammonia solution with a concentration of 9.8 mol / L and a sodium hydroxide solution with a concentration of 11 mol / L were also prepared.

[0147] While stirring at 600 rpm, the above-mentioned ammonia solution was added to deionized water at 60°C, controlling the ammonia concentration to 3.0 g / L. Then, an 11 mol / L sodium hydroxide aqueous solution was passed into the solution to adjust the pH to 11.70. High-purity nitrogen gas was then introduced below the liquid surface at a flow rate of 0.3 m³ / h. 3 / h, to obtain the base liquid;

[0148] A raw material system comprising the above-mentioned ammonia water, the above-mentioned sodium hydroxide aqueous solution, and the metal salt solution is introduced into the bottom liquid. The reaction system is subjected to a first coprecipitation reaction at an ammonia value A1 of 3.0 g / L, a pH value B1 of 11.70, and a flow rate of the metal salt solution C1 of 1.5 L / h to obtain the first product.

[0149] D of the first product 50 After reaching 1.2 μm, the ammonia value of the reaction system was gradually increased to 6.0 g / L, the pH of the reaction system was gradually decreased to 11.45, and the flow rate C2 of the metal salt solution was controlled at 4.0 L / h to allow the reaction system to undergo a second coprecipitation reaction and obtain the second product.

[0150] The second product D 50 Once the depth of precipitation reaches 3.0 μm, the second coprecipitation reaction is stopped.

[0151] Then, after aging the reaction solution of the second coprecipitate, it was first washed by centrifugation with a 10 mol / L hot alkaline solution for 20 min, then washed by centrifugation with hot water for 40 min, then dried at 130℃ for 20 h, and then sieved through a 325 mesh sieve to remove iron, thus obtaining the doped cathode precursor of this embodiment.

[0152] In other words, Comparative Example 5 only underwent the first and second coprecipitation reactions, while other conditions remained unchanged from Example 1.

[0153] Comparative Example 6

[0154] This comparative example provides a method for preparing a doped cathode precursor, including:

[0155] Nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate, and deionized water were mixed to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn=88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; an ammonia solution with a concentration of 9.8 mol / L and a sodium hydroxide solution with a concentration of 11 mol / L were also prepared.

[0156] While stirring at 600 rpm, the above-mentioned ammonia solution was added to deionized water at 60°C, controlling the ammonia concentration to 3.0 g / L. Then, an 11 mol / L sodium hydroxide aqueous solution was passed into the solution to adjust the pH to 11.70. High-purity nitrogen gas was then introduced below the liquid surface at a flow rate of 0.3 m³ / h. 3 / h, to obtain the base liquid;

[0157] A raw material system comprising the above-mentioned ammonia water, the above-mentioned sodium hydroxide aqueous solution, and the metal salt solution is introduced into the bottom liquid. The reaction system is subjected to a first coprecipitation reaction at an ammonia value A1 of 3.0 g / L, a pH value B1 of 11.70, and a flow rate of the metal salt solution C1 of 1.5 L / h to obtain the first product.

[0158] D of the first product 50After reaching 1.2 μm, the reaction system was subjected to a third coprecipitation reaction at an ammonia value of 6.0 g / L, a pH value of 11.45, and a metal salt solution flow rate of 7.5 L / h. The third coprecipitation reaction was stopped when the product particle size reached 3.4 μm.

[0159] Then, after aging the reaction solution of the third coprecipitation, it was first centrifuged and washed for 20 min with a 10 mol / L hot alkaline solution, then centrifuged and washed for 40 min with hot water, then dried at 130℃ for 20 h, and then sieved through a 325 mesh sieve to remove iron, thus obtaining the doped positive electrode precursor of this embodiment.

[0160] In other words, Comparative Example 6 only underwent the first and third coprecipitation reactions, while other conditions remained unchanged from Example 1.

[0161] Comparative Example 7

[0162] This comparative example provides a method for preparing a doped cathode precursor, including:

[0163] Nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate, and deionized water were mixed to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn=88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; an ammonia solution with a concentration of 9.8 mol / L and a sodium hydroxide solution with a concentration of 11 mol / L were also prepared.

[0164] While stirring at 500–700 rpm, the above-mentioned ammonia solution was added to deionized water at 60°C, controlling the ammonia concentration to be 2.5–3.5 g / L. Then, an 11 mol / L sodium hydroxide aqueous solution was passed into the solution to adjust the pH to 11.6–11.80. High-purity nitrogen gas was then introduced below the liquid surface at a flow rate of 0.3 m³ / h. 3 / h, to obtain the base liquid;

[0165] A raw material system comprising the above-mentioned ammonia water, the above-mentioned sodium hydroxide aqueous solution, and the metal salt solution is introduced into the bottom liquid. The ammonia value of the reaction system is gradually increased to 6.0 g / L, and the pH of the reaction system is gradually decreased to 11.45. The flow rate C2 of the metal salt solution is controlled at 4.0 L / h to allow the reaction system to undergo a second coprecipitation reaction and obtain the second product.

[0166] The second product D 50 After reaching 1.5 μm, the reaction system was subjected to a third coprecipitation reaction at an ammonia value of 6.0 g / L, a pH value of 11.45, and a metal salt solution flow rate of 7.5 L / h. The third coprecipitation reaction was stopped when the product particle size reached 3.1 μm.

[0167] Then, after aging the reaction solution of the third coprecipitation, it was first centrifuged and washed for 20 min with a 10 mol / L hot alkaline solution, then centrifuged and washed for 40 min with hot water, then dried at 130℃ for 20 h, and then sieved through a 325 mesh sieve to remove iron, thus obtaining the doped positive electrode precursor of this embodiment.

[0168] In other words, Comparative Example 7 only underwent the second and third coprecipitation reactions, while other conditions remained unchanged from Example 1.

[0169] Experimental Example 1

[0170] The following parameters of the doped cathode precursors of each embodiment and comparative example were tested:

[0171] 1) Morphological characteristics: Figure 1 is a cross-sectional view of the doped cathode precursor of Example 1; Figure 2 is a scanning electron microscope (SEM) image of the first product in Example 1; Figure 3 is a layer SEM image of the second product in Example 1; Figure 4 is a SEM image of the doped cathode precursor of Example 1 at one magnification; Figure 5 is a SEM image of the doped cathode precursor of Example 1 at another magnification; Energy dispersive spectroscopy (EDS) analysis of the doped cathode precursor of Example 1 is shown in Figures 7-10; SEM images of the cathode precursor of Comparative Example 1 at different magnifications are shown in Figures 6, 11, and 12; SEM images of the doped cathode precursor of Comparative Example 2 at different magnifications are shown in Figures 13 and 14; SEM image of the doped cathode precursor of Comparative Example 4 is shown in Figure 15.

[0172] 2)D 50 SPAN: Tested using a Malvern 3000 particle size analyzer. 90 D 10 D 50 Then calculate SPAN according to the following formula: SPAN = (D 90 -D 10 ) / D 50 .

[0173] 3) Tap density (TD): Tested using a tap density meter.

[0174] 4) Specific surface area: tested using a McSurface Area Analyzer.

[0175] 5) Doping amount (unit: ppm): Tested by inductively coupled plasma atomic emission spectrometry (ICP).

[0176] 6) Porosity of the inner, middle, and outer layers, and porosity of the doped cathode precursor (cathode precursor):

[0177] The prepared precursor sample was photographed with SEM cross-sectional images. The sum of the pore areas of the inner layer, the middle layer, and the outer layer on the cross-section was calculated using Metis software. The sum of the pore areas on the precursor cross-section and the cross-sectional area of ​​the cross-section were also calculated. The porosity of the inner layer, the middle layer, and the outer layer, as well as the porosity of the doped cathode precursor (cathode precursor), were calculated according to the formula: porosity = sum of pore areas / cross-sectional area × 100%.

[0178] 7) The thickness of primary particles in the inner, middle and outer layers, the number of nanosheet layers, the radial dimensions R1, R2 and R3 of the inner, middle and outer layers, and the length of the radial channels in the outer layer: Based on the scanning electron microscope images, the above indicators were measured using the measurement software Nano Measurer 1.2.

[0179] 8) Sphericity of the doped cathode precursor: The precursor particles in the SEM were scanned using Metis software to obtain the projected area S and perimeter L. The sphericity R was calculated using the formula: R = 4πS / (L×2).

[0180] Test results

[0181] Table 1. Porosity (%), Radial Channel Length (nm), and Sphericity of Inner Layer, Middle Layer, Outer Layer, and Doped Cathode Precursor

[0182] As can be seen from Table 1, the doped cathode precursor of this application embodiment has a three-layer structure, and the porosity satisfies the following: the porosity of the inner layer is greater than that of the middle layer, the porosity of the middle layer is less than or equal to that of the outer layer, and the outer layer includes radial channels.

[0183] Table 2

[0184] Table 2 shows the SPAN, tap density TD, specific surface area, and D for each embodiment and comparative example. 50 Data such as doping amount.

[0185] Table 3

[0186] As shown in Table 3, the doped cathode precursors in each embodiment are divided into an inner layer, a middle layer, and an outer layer. The inner layer has a loose, porous honeycomb structure, while the middle layer has the densest primary particle packing. The primary particles in the outer layer are oriented to form longitudinal lithium-ion channels, and the outer layer region is relatively dense. Furthermore, the radial dimension R1 of the inner layer in the doped cathode precursors of the above embodiments can be 0.4–1.5 μm, preferably 0.6–1.3 μm, and the ratio of the radial dimension R1 of the inner layer to the diameter of the doped cathode precursor particles can be 25–50%.

[0187] Figure 1 is a cross-sectional view of the doped cathode precursor of Example 1. It can be clearly seen that the doped cathode precursor is divided into an inner layer, a middle layer, and an outer layer. The inner layer has a loose and porous honeycomb structure, while the middle layer has the densest primary particle stacking. The primary particles in the outer layer are oriented to form vertical lithium-ion channels, and the outer layer region is relatively dense. Figure 2 is a scanning electron microscope (SEM) image of the first product in Example 1. The primary particles of the first product are relatively thin, with a thickness of about 10-50 nm. The primary particles are formed by the stacking of 2-10 nanosheets, which are interwoven with each other and have many gaps. Figure 3 is a SEM image of the second product in Example 1. Its primary particles are relatively thick, with a thickness of about 400-600 nm. The primary particles are formed by the stacking of 80-120 nanosheets, which are staggered and densely packed with no obvious gaps. The middle layer has the densest structure. Figures 4-5 are scanning electron microscope (SEM) images of the doped cathode precursor of Example 1. The primary particles are approximately 300-400 nm thick and are formed by the stacking of 60-80 nanosheets. The primary particles exhibit good uniformity and directional arrangement, forming directional channels. The secondary spherical particles have a uniform particle size distribution and good sphericity. Figures 7-10 are energy dispersive spectral mappings (cross-sectional EDS-mapping spectra) of nickel, cobalt, manganese, and zirconium in the doped cathode precursor of Example 1. Specifically, Figure 7 shows the energy dispersive spectral mapping of nickel in the doped cathode precursor of Example 1, where the scale bar (marked as 10 μm) in the lower left corner indicates the actual length of the scale bar segment is 10 μm; Figure 8 shows the energy dispersive spectral mapping of cobalt in the doped cathode precursor of Example 1, where the scale bar (marked as 10 μm) in the lower left corner indicates the actual length of the scale bar segment is 10 μm. The actual length of the line segment is 10 μm; Figure 9 is the energy spectrum mapping diagram of manganese in the doped cathode precursor of Example 1. The scale bar in the lower left corner (marked as 10 μm) indicates that the actual length of the scale line segment is 10 μm; Figure 10 is the energy spectrum mapping diagram of zirconium doped in the doped cathode precursor of Example 1. The scale bar in the lower left corner (marked as 10 μm) indicates that the actual length of the scale line segment is 10 μm. It can be seen from Figure 10 that the doped zirconium is uniformly distributed with no obvious regional differences.Figures 6, 11, and 12 are scanning electron microscope (SEM) images of the cathode precursor of Comparative Example 1. Compared with Example 1, the cathode precursor of Comparative Example 1 without Zr doping, although lacking obvious small particles, exhibits poor whisker uniformity, poor sphericity, and significant multi-head phenomenon. This indicates that Zr doping can significantly improve whisker uniformity and alleviate particle agglomeration. The scale bar in the lower right corner of Figure 11 (marked as 10 μm) indicates the actual length of the scale line segment is 10 μm, and the scale bar in the lower right corner of Figure 12 (marked as 1 μm) indicates the actual length of the scale line segment is 1 μm. Figures 13 and 14 are SEM images of the doped cathode precursor of Comparative Example 2. Compared with Example 1, the doped precursor prepared under low ammonia conditions throughout the process has more small particles. This leads to differences in the size of the lithium diffusion path during the sintering of the cathode active material, affecting sintering uniformity. The presence of high salt concentration in the precursor prepared under low ammonia conditions has an adverse effect on battery performance. The whiskers of the precursor prepared under low ammonia conditions are relatively fine, about 160 nm. The scale bar in the lower right corner of Figure 13 (marked as 30 μm) indicates that the actual length of the scale bar segment is 30 μm. The scale bar in the lower right corner of Figure 14 (marked as 1 μm) indicates that the actual length of the scale bar segment is 1 μm. Figure 15 is a scanning electron microscope image of the doped cathode precursor of Comparative Example 4. Compared with Example 1, the precursor prepared under high salt concentration in the early stage has severe agglomeration, many small particles, poor sphericity, and obvious multi-head phenomenon. However, the doped cathode precursor of Example 1 prepared by the gradient feed flow process has significantly better sphericity, indicating that the gradient feed flow process is beneficial to the improvement of sphericity. The scale bar in the lower right corner of Figure 15 (marked as 10 μm) indicates that the actual length of the scale bar segment is 10 μm.

[0188] Experimental Example 2

[0189] The preparation of positive electrode active materials using the doped positive electrode precursors of the above embodiments and comparative examples specifically includes the following steps: the positive electrode active material is obtained by sintering the above doped positive electrode precursors and lithium carbonate in a certain proportion.

[0190] 1) Morphological characteristics: The cross-section, inner layer, middle layer, and outer layer of the positive electrode active material of Example 1 were scanned by electron microscopy, as shown in Figure 16.

[0191] 2) Porosity of inner, middle, and outer layers, and porosity of the positive electrode active material: SEM cross-sectional images of the prepared positive electrode active material were taken. Metis software was used to process the images to calculate the sum of pore areas of the inner layer, the middle layer, and the outer layer, as well as the sum of pore areas on the precursor cross-section and the cross-sectional area of ​​that cross-section. The porosity of the inner, middle, and outer layers, and the porosity of the positive electrode active material, were calculated using the formula: Porosity = Sum of pore areas / Cross-sectional area × 100%. The results are shown in Table 4.

[0192] 3) Length of radial channel: Based on the scanning electron microscope image, the above parameters were measured using the Nano Measurer 1.2 software.

[0193] Table 4

[0194] As can be seen from Figure 16 and the table above, the positive electrode active material of this application embodiment has a three-layer structure, and the porosity satisfies the following: the porosity of the inner layer is greater than that of the middle layer, the porosity of the middle layer is less than or equal to that of the outer layer, and the outer layer includes radial channels.

[0195] Experimental Example 3

[0196] The positive electrode active materials corresponding to the examples and comparative examples in Experimental Example 2 were prepared into positive electrode sheets and assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain coin cells. The method includes: mixing each positive electrode active material with conductive carbon black (SP) and PVDF in a weight ratio of 80%:10%:10% to obtain a positive electrode slurry by dispersion. The slurry is coated on an aluminum foil current collector and rolled to obtain a positive electrode sheet. Then, the positive electrode sheet is punched into small discs with a diameter of 12 mm using a film die. After drying and weighing, in a glove box under an Ar protective atmosphere, using a 2025 coin cell case, a Li metal disc is used as the negative electrode. The electrolyte includes LiPF6 and a solvent, wherein the concentration of LiPF6 in the electrolyte is 1.0 M, and the solvent includes EC and DMC in a volume ratio of 1:1. The above positive electrode sheet (small discs after drying and weighing), negative electrode, electrolyte, and 2025 coin cell case are assembled together to form a coin cell.

[0197] 1) After each coin cell was left to stand for 4 hours under normal conditions, the charge and discharge capacity of the battery was tested according to the following steps: charge to 4.55V at 0.2C, charge at constant voltage to 0.025C and then let stand for 3 minutes, then discharge to 3.0V at 0.2C. Obtain the charge and discharge curves and record the first charge capacity C0 and the first discharge capacity D0.

[0198] 2) Test the battery's cycle performance according to the following steps: At 25°C, charge at a constant current rate of 1C to 4.50V, then charge at a constant voltage rate of 0.05C to 4.50V, and then discharge at a discharge rate of 1C to 3.0V. Repeat this charge-discharge cycle 200 times. Measure the discharge capacity Q1 at the first cycle and the discharge capacity Q at the 200th cycle. 200 The capacity retention rate Q after 200 cycles is calculated using the following formula: Capacity retention rate Q = Q 200 / Q1*100%. See Table 5 for relevant data.

[0199] Table 5 Test results of button cells

[0200] The electrochemical performance analysis results of the various embodiments and comparative examples show that the doped cathode precursor of the present application can have both good cycle performance and capacity.

[0201] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A doped cathode precursor, characterized in that, The doped cathode precursor comprises, in a radial direction from the inside out, an inner layer, an intermediate layer, and an outer layer. The porosity of the inner layer is greater than that of the intermediate layer, the porosity of the intermediate layer is less than or equal to that of the outer layer, and the outer layer includes radial channels.

2. The doped cathode precursor according to claim 1, characterized in that, The porosity of the inner layer is 10% to 15%, the porosity of the middle layer is 1% to 5%, and the porosity of the outer layer is 5% to 10%.

3. The doped cathode precursor according to claim 1 or 2, characterized in that, The porosity of the doped cathode precursor is 2% to 8%; And / or, the radial dimensions of the inner layer, the intermediate layer and the outer layer are R1, R2 and R3, respectively, where R1 is 0.6 to 1.3 μm, R2 is 0.4 to 0.8 μm and R3 is 0.3 to 0.8 μm.

4. The doped cathode precursor according to any one of claims 1-3, characterized in that, The thickness of the primary particles in the inner layer is 10-50 nm, the thickness of the primary particles in the middle layer is 400-600 nm, and the thickness of the primary particles in the outer layer is 300-400 nm.

5. The doped cathode precursor according to any one of claims 1-4, characterized in that, The chemical formula of the doped cathode precursor is: (Ni a Co b Mn c M d (OH)2, wherein 0.8≤a<1.0, 0<b≤0.1, 0<c≤0.1, a+b+c+d=1, 0<d≤0.05, and M includes one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo; And / or, the mass percentage of doping elements in the doped cathode precursor is 1000 to 8000 ppm; And / or, the tap density of the doped cathode precursor is 1.7–2.0 g / cm³. 3 ; And / or, the specific surface area of ​​the doped cathode precursor is greater than or equal to 4 m². 2 / g and less than 10m 2 / g; And / or, the D of the doped cathode precursor 50 The micrometer ranges from 3.0 to 4.0 μm, while the span ranges from 0.6 to 1.2 μm. And / or, the length of the radial channel is 90–220 nm; And / or, the sphericity of the doped cathode precursor is greater than or equal to 0.9 and less than 1.

0.

6. A method for preparing a doped cathode precursor according to any one of claims 1-5, characterized in that, include: A raw material system comprising ammonia, alkaline solution, and metal salt solution is introduced into the bottom liquid, and the reaction system undergoes a first coprecipitation reaction at an ammonia value of A1, a pH of B1, and a flow rate of metal salt solution of C1 to obtain the first product. D of the first product 50 After reaching the expected particle size, the ammonia value of the reaction system is gradually increased, the pH of the reaction system is decreased, and the flow rate of the metal salt solution is controlled to C2, so that the reaction system undergoes a second coprecipitation reaction to obtain the second product. The second product D 50 After the desired particle size is achieved, the reaction system is subjected to a third coprecipitation reaction at an ammonia value of A3, a pH of B3, and a metal salt solution flow rate of C3 to obtain the doped cathode precursor; wherein, A1 < A3, B1 > B3, and C1 < C2 < C3.

7. The method for preparing the doped cathode precursor according to claim 6, characterized in that, A1 is 2.5–3.5 g / L, and A3 is 5.5–6.5 g / L; And / or, B1 is 11.60–11.80, and B3 is 11.40–11.50; And / or, C1 is 1.0–2.0 L / h, C2 is 3.5–4.5 L / h, and C3 is 7.0–8.0 L / h.

8. The method for preparing the doped cathode precursor according to claim 6 or 7, characterized in that, The ammonia value of the substrate solution is 1-4 g / L, and the pH is 11.6-12.

0. And / or, the temperature of the reaction system is 40–70°C; And / or, the metal salt solution comprises a mixed solution of nickel, cobalt, and manganese with a total molar concentration of 1.0 to 2.5 mol / L, wherein the molar ratio of nickel, cobalt, and manganese is a:b:c, 0.8≤a<1.0, 0<b≤0.1, 0<c≤0.1, and a+b+c=1; And / or, the metal salt solution includes a dopant element, which includes one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo.

9. A positive electrode active material, characterized in that, The positive electrode active material is a doped positive electrode active material. The positive electrode active material includes an inner layer, an intermediate layer and an outer layer in the radial direction from the inside to the outside. The porosity of the inner layer is greater than that of the intermediate layer. The porosity of the intermediate layer is less than or equal to that of the outer layer. The outer layer includes radial channels.

10. The positive electrode active material according to claim 9, characterized in that, The positive electrode active material is formed from the doped positive electrode precursor according to any one of claims 1-5 or the doped positive electrode precursor prepared according to the preparation method according to any one of claims 6-8.

11. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive electrode active material as described in claim 9 or 10.

12. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in claim 11.

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