High-nickel ternary positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application discloses high-nickel ternary positive electrode material and a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion batteries.The application adopts a method for modifying high-nickel ternary positive electrode material by gradient aluminum doping, a lower concentration of aluminum is doped in the material in primary sintering to form uniform doping (the doped aluminum mass concentration and the coated aluminum mass concentration satisfy the relationship of formula 1), the aluminum element coating concentration, the sintering temperature of secondary sintering, and the material D50 and the primary particle size satisfy the relationship of formula 2 of sintering time, so that a gradient distribution structure of the aluminum element is formed, the concentration of the aluminum element continuously decreases from the surface to the inside of the material, and the industry pain points of capacity loss caused by traditional uniform doping, easy peeling and failure of a single coating layer, structural collapse of high-nickel material in the cycle process, and high risk of thermal runaway are solved from the root, and the synergistic improvement of high specific capacity, long cycle life and high safety of the high-nickel positive electrode material is realized.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to high-nickel ternary cathode materials, their preparation methods, and lithium-ion batteries. Background Technology

[0002] High-nickel ternary cathode materials (usually referring to NCM / NCA materials with a nickel content ≥80%) have become one of the mainstream cathode materials for next-generation power and energy storage batteries due to their high specific capacity, high voltage platform, and cost advantages. However, high-nickel ternary materials still have the following main problems: (1) Insufficient structural stability of high-nickel ternary materials. During charge-discharge cycles, high-nickel materials undergo multiple phase transitions (especially the H2→H3 phase transition), accompanied by strong anisotropic lattice contraction and expansion, generating huge internal stresses within the secondary particles, which in turn lead to microcracks or even pulverization of the particles. These microcracks expose new active surfaces, accelerating the side reactions between the electrolyte and electrode materials, and at the same time causing the integrity of the electrode structure to be destroyed, ultimately resulting in rapid capacity decay of the battery.

[0003] (2) High-nickel ternary materials have poor thermal safety. High-nickel materials contain Ni in a high oxidation state. 4+ It has strong oxidizing properties and easily reacts with electrolytes. At the same time, the lattice oxygen activity on the surface of the material is high, and it easily releases oxygen when heated, which can cause electrolyte decomposition, gas production, or even thermal runaway, posing serious safety hazards.

[0004] (3) High-nickel materials have many surface defects and prominent lithium-nickel mixing problems, which will further aggravate the increase of interface impedance and irreversible capacity loss, resulting in a significant decrease in the rate performance and cycle life of the material.

[0005] To address the aforementioned issues, existing technologies primarily employ modification methods such as doping, coating, or constructing core-shell gradient structures. While uniform elemental doping can enhance lattice stability to some extent, achieving the desired modification effect typically requires a high doping concentration, which directly reduces the internal nickel content and sacrifices the material's specific capacity. Single-surface coatings (such as oxide or phosphate coatings) can, to some extent, prevent electrolyte erosion, but only address surface issues and cannot improve inherent defects in the bulk lattice. Furthermore, the coating layer is prone to cracking and detachment during long-term cycling, making the modification effect unsustainable. Conventional core-shell gradient structures can balance high internal capacity with high external stability, but abrupt changes in elemental concentrations can lead to interfacial stress mismatch, making microcracks more likely to form during cycling, thus failing to fundamentally solve the stability problem of high-nickel materials.

[0006] Therefore, the industry urgently needs a new modification technology that can simultaneously achieve bulk lattice stability, surface interface protection, and long-term cycle stability without sacrificing the high specific capacity advantage of high-nickel materials, thereby fundamentally solving the structural failure and safety issues of high-nickel ternary cathode materials.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] The purpose of this invention is to provide a high-nickel ternary cathode material, its preparation method, and a lithium-ion battery, aiming to improve long-term cycle stability without sacrificing the high specific capacity advantage of high-nickel materials.

[0009] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a high-nickel ternary cathode material, comprising: mixing a ternary precursor, a lithium source and a first aluminum source to obtain a first mixture; The first mixture is sintered once to obtain a modified material; The primary modified material is mixed with the second aluminum source to obtain a second mixture; The second mixture is subjected to secondary sintering to obtain the modified product; Wherein, the mass fraction of aluminum element introduced from the first aluminum source in the modified product is W1, and the mass fraction of aluminum element introduced from the second aluminum source in the modified product is W2, and W1 and W2 satisfy: Formula 1; The sintering time t for secondary sintering satisfies: Formula 2; In the formula, the unit of t is h; D 50 The average particle size of the secondary particles in the primary modified material is expressed in μm. d represents the average grain size of the primary particles in the primary modified material, in nm; T represents the sintering temperature of the secondary sintering, in °C.

[0010] In an optional implementation, the parameters in Equations 1 and 2 satisfy the following: 0.5%≤W2≤1.2%; 180nm≤d≤350nm; 8.0μm≤D50≤13.0μm; 580℃≤T≤710℃.

[0011] In an optional embodiment, the first aluminum source and the second aluminum source are each independently selected from at least one of aluminum hydroxide, aluminum oxide, aluminum phosphate, aluminum sulfate, aluminum oxalate, aluminum acetate and aluminum citrate; Preferably, the first aluminum source is selected from aluminum hydroxide; The second aluminum source is selected from aluminum citrate.

[0012] In an optional embodiment, the step of preparing the first mixture includes: mixing the ternary precursor, the lithium source, the first aluminum source, and the magnesium source; Preferably, by adjusting the amount of lithium source added, the molar ratio of lithium to the total amount of nickel, cobalt, and manganese in the ternary precursor is 1.04-1.08. Preferably, the amount of magnesium source is adjusted so that the mass fraction of magnesium in the modified product is 0.05%-0.20%; more preferably, the magnesium source is selected from at least one of magnesium acetate, magnesium oxide, magnesium hydroxide, magnesium sulfate and magnesium carbonate. Preferably, during the preparation of the first mixture, the stirring rate is controlled at 700 rpm-900 rpm, the mixing time is 40 min-60 min, and the mixing temperature is 25℃-45℃.

[0013] In an optional embodiment, the ternary precursor is nickel cobalt manganese hydroxide with the chemical formula NixCoyMnz(OH)2, where 0.80≤x≤0.98 and x+y+z=1.

[0014] In an optional embodiment, the first sintering step includes: first holding at 400℃-600℃ for 1h-3h, and then holding at 750℃-800℃ for 10h-15h. Preferably, the heating rate for a single sintering is controlled to be 2℃ / min-4℃ / min; Preferably, the primary sintering is carried out in an oxygen-containing atmosphere, and after sintering, the material is cooled and passed through a 400-mesh sieve to obtain the primary modified material.

[0015] In an optional embodiment, the step of preparing the second mixture includes: mixing the primary modified material, the second aluminum source, and the cobalt source; Preferably, the amount of cobalt source added is controlled so that the mass fraction of cobalt in the modified product is 0.4%-0.8%; Preferably, the cobalt source is selected from at least one of cobalt tetroxide, cobalt hydroxide, cobalt sulfate, cobalt chloride, cobalt carbonate, and cobalt nitrate; Preferably, during the preparation of the second mixture, the stirring rate is controlled at 600 rpm-800 rpm, the mixing time is 30 min-60 min, and the mixing temperature is 25℃-45℃.

[0016] In an optional embodiment, the secondary sintering is carried out in an oxygen-containing atmosphere, and after sintering, the temperature is lowered and then sieved and iron is removed. And / or, control the heating rate of the secondary sintering to be 2℃ / min-4℃ / min.

[0017] Secondly, the present invention provides a high-nickel ternary cathode material, which is prepared by any of the preparation methods described in the foregoing embodiments.

[0018] Thirdly, the present invention provides a lithium-ion battery comprising the high-nickel ternary cathode material described in the foregoing embodiments.

[0019] This invention has the following beneficial effects: This invention adopts a method for modifying high-nickel ternary cathode materials with gradient aluminum doping. In the first sintering, a low concentration of aluminum doping is used to form uniform doping inside the material (the mass concentration of doped aluminum and the mass concentration of coated aluminum satisfy the relationship in Equation 1). In the second sintering, by limiting the aluminum element coating concentration, the sintering temperature of the second sintering, and the relationship between the material D50 and the first particle size satisfying the sintering time in Equation 2, a gradient distribution structure in which the concentration of aluminum element continuously decreases from the surface to the interior of the material is formed. This fundamentally solves the industry pain points caused by traditional uniform doping, such as capacity loss, easy detachment and failure of a single coating layer, and high risk of structural collapse and thermal runaway during cycling of high-nickel materials. It achieves a synergistic improvement in high specific capacity, long cycle life and high safety of high-nickel cathode materials.

[0020] It should be noted that only when Equation 1 is satisfied can a small amount of aluminum ions diffuse into the material during the first high-temperature treatment, pre-forming a uniform doped structure to stabilize the lattice oxygen and improve the structural stability of the material. However, when the subsequent coating with a higher concentration of aluminum citrate satisfies Equation 2 at sintering time t, the heat treatment process causes the aluminum source, such as aluminum citrate, to first decompose into aluminum ions and carbon chain organic molecules. Subsequently, with increasing temperature and treatment time, aluminum ions gradually diffuse into the material's interior. Equation 2 ensures that the reaction time reaches the optimal matching state for the material, resulting in some aluminum gradually penetrating and doping into the shallow, middle, and deep layers of the material, while some aluminum remains coated on the surface and forms a conductive carbon-alumina composite coating with the carbon chains. Ultimately, this results in a gradient doped structure with the aluminum element concentration gradually increasing from the inside out. If time t is too low, the structure formed is mainly aluminum coating, and the internal gradient doped structure is not fully formed, reducing the material's specific capacity and thermal safety performance. If time t is too high, the structure formed is mainly aluminum doping, and most of the aluminum in the second sintering is doped into the material's interior, reducing the material's specific capacity and cycle performance.

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a complete SEM image of the high-nickel cathode material from Example 1; Figure 2 The graphs show the first charge-discharge performance of the button batteries in Example 1 and Comparative Example 1. Figure 3 The graphs show the charge-discharge cycle performance of the button batteries in Example 1 and Comparative Example 1 at 45°C. Figure 4 The DSC spectra are those of Example 1 and Comparative Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] To fundamentally address the stability issues of high-nickel materials, this invention employs a gradient aluminum doping modification method to form a gradient distribution structure in which the concentration of aluminum continuously decreases from the material surface to the interior. This fundamentally solves the industry pain points caused by traditional uniform doping, such as capacity loss, easy detachment and failure of a single coating layer, and high risk of structural collapse and thermal runaway during cycling of high-nickel materials. It achieves a synergistic improvement in high specific capacity, long cycle life, and high safety of high-nickel cathode materials.

[0026] This invention provides a method for preparing a high-nickel ternary cathode material, comprising the following steps: S1, One-time mixing The ternary precursor, lithium source, and first aluminum source are mixed evenly to obtain the first mixture.

[0027] In some embodiments, the ternary precursor is nickel-cobalt-manganese hydroxide with the chemical formula NixCoyMnz(OH)2, where 0.80 ≤ x ≤ 0.98 and x + y + z = 1. Specifically, the value of x can be 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, etc., and the maximum value of y and z is less than 0.2, while the minimum value is greater than 0. By controlling the particle size D50 of the ternary precursor, the particle size D50 of the final product is made to meet the requirement of 8.0 μm-13.0 μm. Generally, the particle size D50 of the ternary precursor is larger than the particle size D50 of the final product, with a difference of 0.5-1.5 μm.

[0028] Furthermore, by adjusting the amount of lithium source added, the molar ratio (Li / Me) of lithium to the total amount of nickel, cobalt, and manganese in the ternary precursor can be made to be 1.04-1.08, such as 1.04, 1.05, 1.06, 1.07, 1.08, etc. The type of lithium source is not limited, such as battery-grade lithium hydroxide, but is not limited to this.

[0029] In some embodiments, the first aluminum source is selected from at least one of aluminum hydroxide, alumina, aluminum phosphate, aluminum sulfate, aluminum oxalate, aluminum acetate, and aluminum citrate. The first aluminum source can be any one or more of the above, preferably aluminum hydroxide. The amount of the first aluminum source added is controlled according to the description of step S4 in the specification.

[0030] To further improve product performance, a magnesium source is introduced during the preparation of the first mixture. The ternary precursor, lithium source, first aluminum source, and magnesium source are mixed uniformly to obtain the first mixture. By adjusting the amount of magnesium source, the mass fraction of magnesium in the modified product is made to be 0.05%-0.20%, such as 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, etc. Preferably, the magnesium source is selected from at least one of magnesium acetate, magnesium oxide, magnesium hydroxide, magnesium sulfate, and magnesium carbonate, and the magnesium source can be any one or more of the above.

[0031] To improve the uniformity of the mixture, during the preparation of the first mixture, the stirring speed should be controlled at 700 rpm-900 rpm, such as 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, etc.; the mixing time should be 40 min-60 min, such as 40 min, 45 min, 50 min, 55 min, 60 min, etc.; and the mixing temperature should be 25℃-45℃, such as 25℃, 30℃, 35℃, 40℃, 45℃, etc. The mixing equipment is not limited; a high-speed mixer can be used.

[0032] S2, First sintering The first mixture is sintered once to obtain a modified material. The sintering equipment is not limited; a general sintering furnace can be used. The first mixture is loaded into a sagger, perforated, and then sintered once in a kiln.

[0033] In some embodiments, the primary sintering step includes: first holding at 400℃-600℃ for 1h-3h, and then holding at 750℃-800℃ for 10h-15h. The primary sintering is divided into two stages. The temperature of the first stage can be 400℃, 450℃, 500℃, 550℃, 600℃, etc.; the holding time of the first stage can be 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, etc.; the temperature of the second stage can be 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, etc.; the holding time of the second stage can be 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0034] Furthermore, the heating rate of the first sintering is controlled to be 2℃ / min-4℃ / min, such as 2℃ / min, 3℃ / min, 4℃ / min, etc. The first sintering is carried out in an oxygen-containing atmosphere (such as oxygen). After sintering, the material is cooled and passed through a 400-mesh sieve to obtain the primary modified material.

[0035] S3, Secondary Mixing The modified material is mixed evenly with the second aluminum source to obtain a second mixture, which is ready to proceed to step S4 for secondary sintering. The amount of the second aluminum source added is as described in step S4 of the instruction manual.

[0036] In some embodiments, the second aluminum source is selected from at least one of aluminum hydroxide, aluminum oxide, aluminum phosphate, aluminum sulfate, aluminum oxalate, aluminum acetate, and aluminum citrate. The second aluminum source can be any one or more of the above, preferably aluminum citrate. The heat treatment process causes aluminum citrate to first decompose into aluminum ions and carbon chain organic molecules. Subsequently, as the temperature increases and the treatment time increases, the aluminum ions gradually diffuse into the interior of the material, forming a partial aluminum that gradually penetrates and dops into the shallow, middle, and deep layers of the material. Some aluminum remains coated on the material surface and forms a conductive carbon-alumina composite coating layer with the carbon chains, ultimately forming a gradient doping structure in which the concentration of aluminum gradually increases from the inside to the outside.

[0037] In some embodiments, to further improve product performance, surface cobalt doping is introduced. The step of preparing the second mixture includes: uniformly mixing the primary modified material, the second aluminum source, and the cobalt source. The amount of cobalt source added is controlled so that the mass fraction of cobalt in the modified product is 0.4%-0.8%, such as 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc. The cobalt source is selected from at least one of cobalt tetroxide, cobalt hydroxide, cobalt sulfate, cobalt chloride, cobalt carbonate, and cobalt nitrate; the cobalt source can be any one or more of the above.

[0038] In some embodiments, during the preparation of the second mixture, the stirring rate is controlled at 600 rpm-800 rpm, such as 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, etc.; the mixing time is 30 min-60 min, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.; and the mixing temperature is 25℃-45℃, such as 25℃, 30℃, 35℃, 40℃, 45℃, etc. The mixing equipment is not limited; a high-speed mixer can be used for mixing.

[0039] S4, Secondary Sintering The second mixture is sintered a second time to obtain the final modified product.

[0040] The inventors specifically optimized the addition amounts of the first and second aluminum sources. The mass fraction of aluminum introduced by the first aluminum source in the modified product is W1, and the mass fraction of aluminum introduced by the second aluminum source in the modified product is W2. W1 and W2 satisfy the following: Formula 1.

[0041] That is, 0.247 W2 ≤ W1 ≤ 0.354 W2 Simultaneously, the sintering time t for the secondary sintering was optimized to satisfy: Formula 2; In the formula, the unit of t is h; D 50The average particle size of the secondary particles in the primary modified material is expressed in μm. Specifically, the average particle size of the secondary particles in the primary modified material can be obtained by testing with a laser particle size analyzer.

[0042] d represents the average grain size of the primary particles in the primary modified material, in nm; specifically, the average grain size of the primary particles can be obtained by SEM testing and manual measurement of the primary particle size using nanomeasurer software.

[0043] T represents the sintering temperature of the secondary sintering, in °C.

[0044] In Equation 2, each parameter only needs to be calculated with a specific unit value; the unit is not involved in the calculation.

[0045] D in expression 2 50 The relationship between d, T and t is actually an empirical rule. The value corresponding to the unit used is substituted into the formula, but the unit does not need to be substituted. This relationship only serves to constrain the sintering conditions and may not have a strict physical meaning. However, this method can be used to accurately calculate the second sintering time required for the material.

[0046] It should be noted that, in this embodiment of the invention, a small amount of Al is incorporated through low-concentration aluminum doping during the first firing stage. 3+ Ni is uniformly introduced into the bulk lattice of the high-nickel ternary cathode material, replacing the transition metal layer. 2+ / Ni 3+ At the site, Al-O covalent bonds are formed with bond energies far exceeding those of Ni-O and Co-O bonds. This strong bonding significantly enhances the rigidity of the layered crystal framework, greatly improves the crystal structure's resistance to deformation, effectively suppresses anisotropic lattice contraction and expansion induced by the H2-H3 phase transition during charging and discharging, and reduces stress concentration and microcrack formation within secondary particles; simultaneously, the doped Al... 3+ With an ionic radius similar to that of transition metal ions, it can form a stable occupying structure. Its steric hindrance effect can effectively suppress Li / Ni cation mixing during cycling, avoiding the irreversible phase transformation of the layered structure to the spinel and rock salt phases caused by mixing. This ensures the integrity of the crystal structure and cycling stability at the bulk level. In addition, the low concentration of bulk doping avoids the excessive crowding of high-nickel active sites by traditional high-concentration uniform doping, maximizing the preservation of the high specific capacity advantage of high-nickel materials and solving the problem of "doping modification inevitably reduces capacity".

[0047] This invention utilizes a two-stage aluminum coating process, combined with precise control of the aluminum concentration, sintering temperature, and holding time, while simultaneously matching the material's D50 and primary particle size. This achieves a gradient distribution of aluminum elements that continuously decreases from the material's surface to its interior, constructing an integrated composite modified structure of "shallow surface doping + dense coating layer." During high-temperature sintering, the high concentration of aluminum on the surface reacts with the matrix to form a stable spinel phase / aluminum-containing composite oxide coating layer, and simultaneously forms a shallow surface doping transition zone, avoiding the abrupt interfacial stress change problem between the traditional coating layer and the matrix material. The mechanism of this composite structure is manifested in three aspects: First, the dense aluminum-containing coating layer acts as a physical barrier, effectively preventing the electrolyte from reacting with the highly active Ni on the material surface. 4+ The direct contact between the coating layer and the substrate material inhibits the catalytic decomposition of the electrolyte and the corrosion of the material by HF, significantly reducing interfacial side reactions and the dissolution of transition metals. Secondly, the strong bonding of Al-O bonds can significantly anchor lattice oxygen, reduce the activity and mobility of lattice oxygen, inhibit oxygen release and structural collapse at high temperatures, thereby significantly increasing the thermal decomposition initiation temperature and peak temperature of the material, reducing the exothermic enthalpy in DSC testing, and effectively improving thermal safety performance. Thirdly, the shallow-layer doped transition region achieves continuous lattice matching between the coating layer and the substrate material, avoiding the defects of traditional coating layers that are prone to cracking and falling off, and ensuring the long-term effectiveness of the modification effect in long-cycle processes.

[0048] Through the synergistic modification of bulk doping and gradient coating, the high-nickel ternary cathode material of this invention achieves significant improvements in multiple performance aspects: In terms of electrochemical performance, the stable bulk lattice structure reduces structural collapse and active lithium loss during cycling, and the gradient distribution of aluminum elements does not significantly increase interfacial impedance, thus improving the material's cycling stability while maintaining no significant rate performance degradation; In terms of thermal safety performance, the strong Al-O bond anchoring effect on lattice oxygen inhibits high-temperature oxygen release, increasing the material's thermal decomposition temperature and significantly reducing the risk of thermal runaway; In terms of structural stability, the gradient distribution of aluminum elements effectively alleviates stress concentration during cycling, avoiding performance degradation caused by particle pulverization.

[0049] In some embodiments, the parameters in Equations 1 and 2 satisfy: 0.5%≤W2≤1.2%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, etc.; 180nm≤d≤350nm, where d is the average grain size of the particles after one pass through sieving, such as 180nm, 200nm, 230nm, 250nm, 280nm, 300nm, 330nm, 350nm, etc.; 8.0μ m≤D50≤13.0μm, where D50 is the particle size of the secondary particles in the first sintering, such as 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10.0μm, 10.5μm, 11.0μm, 11.5μm, 12.0μm, 12.5μm, 13.0μm, etc.; 580℃≤T≤710℃, where T is the second sintering temperature, such as 580℃, 600℃, 630℃, 650℃, 680℃, 700℃, 710℃, etc.

[0050] In some embodiments, the secondary sintering is carried out in an oxygen-containing atmosphere (such as oxygen), and after sintering, the temperature is lowered and then sieved and iron is removed. The heating rate of the secondary sintering is controlled to be 2℃ / min-4℃ / min, such as 2℃ / min, 3℃ / min, 4℃ / min, etc.

[0051] It should be noted that the preparation method provided in this invention is simple, highly operable, and the sintering conditions can be adjusted within the existing mature high-nickel cathode mass production line process framework. No additional equipment modifications or complex process steps are required, making the cost controllable and suitable for large-scale industrial production. This provides an efficient and feasible technical route for preparing high-nickel ternary cathode materials with both high energy density and excellent safety performance. Furthermore, the method involved in this invention optimizes the sintering process at the cathode material end, is simple and widely applicable, and unlike traditional methods for preparing gradient-doped precursors, it does not incur additional costs or involve complex processes. Moreover, the cathode material prepared by this method exhibits higher specific capacity, high-temperature cycling performance, DSC onset temperature, and DSC peak temperature.

[0052] This invention also provides a high-nickel ternary cathode material, which is prepared by the preparation method provided in this invention, and can simultaneously improve the material's capacity, cycle life, and thermal safety performance.

[0053] This invention also provides a lithium-ion battery, including a high-nickel ternary cathode material provided in this invention, a cathode sheet prepared using the high-nickel ternary cathode material, and then assembled with a negative electrode sheet, a separator, and an electrolyte.

[0054] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0055] Example 1 This embodiment also provides a high-nickel ternary cathode material, the preparation process of which is as follows: (1) Weigh Ni according to the molar ratio of lithium source to precursor of Li / Me = 1.06. 0.96 Co 0.03 Mn 0.01 (OH)2 precursor (step (4) modified product D50 is 10-11.0μm) and battery grade lithium hydroxide, and separately weigh 0.2% aluminum hydroxide (controlling the amount of aluminum introduced in step (4) to obtain a mass fraction of 0.2%) and 0.1% magnesium acetate (controlling the amount of magnesium introduced in step (4) to obtain a mass fraction of 0.1%), add them to a high-speed mixer for mixing, the mixing speed is 800rpm, the mixing time is 50min, the mixing temperature is 35℃, and the first mixture is obtained.

[0056] (2) The first mixture is loaded into a sagger, punched, and sintered in a kiln. Under an oxygen atmosphere, the temperature is first raised to 500°C at a rate of 3°C / min, and then held for 2 hours. After that, the temperature is raised to 780°C and held for 12 hours. Then the temperature is lowered and cooled, and the mixture is passed through a 400-mesh sieve to obtain the modified material.

[0057] (3) Weigh 0.6% cobalt tetroxide (controlling the amount of cobalt introduced in step (4) to obtain a mass fraction of 0.6% in the product) and 0.8% aluminum citrate (controlling the amount of aluminum introduced in step (4) to obtain a mass fraction of 0.8% in the product), add them to a high-speed mixer for mixing. The mixing speed is 700 rpm, the mixing time is 40 min, and the mixing temperature is 35℃. After mixing, a second mixture is obtained.

[0058] (4) The second mixture is loaded into a sagger and fired in a kiln. Under an oxygen atmosphere, the temperature is raised to 690°C at a rate of 3°C / min. The second firing holding and sintering time is t (calculated according to formula 2). Then, the mixture is cooled and then screened, iron is removed, and packaged to obtain the modified product.

[0059] Test step (2) yielded the SEM image of the modified material as shown below. Figure 1 As shown, the particle size D50 of the secondary particles in this sample was found to be 10.0 μm by laser particle size analysis. By measuring the 20k images of the particles using nanomeasurer software, 5-10 positive electrode particles were selected and the short side dimensions were measured. Finally, the average grain size d of the primary particles of the primary modified material was found to be 267.5 nm.

[0060] Given D50 = 10 μm, d = 267.5 nm, T = 690 °C, and W2 = 0.8%, substituting these values ​​into Equation 2, we get t = 13.75 h.

[0061] In this embodiment, W1 = W2 / 4 satisfies Equation 1.

[0062] Example 2 The only difference from Example 1 is that in step (1) of Example 1, the magnesium acetate additive is replaced with magnesium fluoride, while the amount of magnesium added remains unchanged.

[0063] Example 3 The only difference from Example 1 is that in step (1) of this example, magnesium acetate is not added, other ratios remain unchanged, Li / Me is still 1.06, and the amount of aluminum introduced is controlled to obtain a mass fraction of 0.2% in the product in step (4).

[0064] Example 4 The only difference from Example 1 is that in step (1) of this example, the particle size of the precursor is changed so that the modified product D50 in step (4) is 8.0-10.0 μm.

[0065] Example 5 The only difference from Example 1 is that in step (1) of this example, the particle size of the precursor is changed so that the modified product D50 in step (4) is a cathode material with a particle size of 11.0-13.0 μm.

[0066] Example 6 The only difference from Example 1 is that in step (3) of this example, the 0.8% aluminum citrate is reduced to 0.57% (calculated by Formula 1).

[0067] In this embodiment, W1 = 0.35W2, which satisfies Equation 1.

[0068] Example 7 The only difference from Example 1 is that in step (3) of this example, the 0.8% aluminum citrate is reduced to 0.67% (calculated by Formula 1).

[0069] In this embodiment, W1 = 0.30W2, which satisfies Equation 1.

[0070] Example 8 The only difference from Example 1 is that in step (3) of this example, 0.6% cobalt tetroxide is replaced with 0.6% cobalt hydroxide, that is, the amount of cobalt introduced is controlled in step (4) to obtain a mass fraction of 0.6% in the product.

[0071] Example 9 The only difference from Example 1 is that no cobalt tetroxide coating agent is added in step (3), and the amount of aluminum added remains unchanged. The amount of aluminum element introduced is controlled to be 0.8% in the mass fraction of the product obtained in step (4).

[0072] Example 10 The only difference from Example 1 is that the parameter values ​​in steps (1)-(4) are different, as follows: (1) Weigh Ni according to the molar ratio of lithium source to precursor of Li / Me = 1.04. 0.96 Co 0.03 Mn 0.01 (OH)2 precursor (D50 of the modified product in step (4) is 8.0-13.0 μm) and battery-grade lithium hydroxide, and separately weigh 0.2% aluminum hydroxide (the amount of aluminum introduced is controlled to be 0.2% by mass in the product obtained in step (4)) and 0.05% magnesium acetate (the amount of magnesium introduced is controlled to be 0.05% by mass in the product obtained in step (4), and add them to a high-speed mixer for mixing. The mixing speed is 700 rpm, the mixing time is 60 min, and the mixing temperature is 25℃ to obtain the first mixture.

[0073] (2) The first mixture is loaded into a sagger, punched, and sintered in a kiln. Under an oxygen atmosphere, the temperature is first raised to 400°C at a rate of 2°C / min, and after heat treatment for 3 hours, the temperature is raised to 750°C and sintered for 15 hours. Then the temperature is lowered and cooled, and the mixture is passed through a 400-mesh sieve to obtain the modified material.

[0074] (3) Weigh 0.4% cobalt tetroxide (controlling the amount of cobalt introduced to obtain a mass fraction of 0.4% in the product in step (4)) and 0.8% aluminum citrate (controlling the amount of aluminum introduced to obtain a mass fraction of 0.8% in the product in step (4)), add them to a high-speed mixer for mixing. The mixing speed is 600 rpm, the mixing time is 60 min, and the mixing temperature is 25℃. After mixing, a second mixture is obtained.

[0075] (4) The second mixture is loaded into a sagger and fired in a kiln. Under an oxygen atmosphere, the temperature is raised to 580°C at a rate of 2°C / min. The second firing holding time is 14.25h (calculated according to formula 2). Then, the mixture is cooled and then screened, iron is removed, and packaged to obtain the modified product.

[0076] Example 11 The only difference from Example 1 is that the parameter values ​​in steps (1)-(4) are different, as follows: (1) Weigh Ni according to the molar ratio of lithium source to precursor of Li / Me = 1.08. 0.96 Co 0.03 Mn 0.01(OH)2 precursor (D50 of the modified product in step (4) is 8.0-13.0 μm) and battery-grade lithium hydroxide, and separately weigh 0.2% aluminum hydroxide (the amount of aluminum introduced is controlled to be 0.2% by mass in the product obtained in step (4)) and 0.20% magnesium acetate (the amount of magnesium introduced is controlled to be 0.20% by mass in the product obtained in step (4), and add them to a high-speed mixer for mixing. The mixing speed is 900 rpm, the mixing time is 40 min, and the mixing temperature is 45℃ to obtain the first mixture.

[0077] (2) The first mixture is loaded into a sagger, punched, and sintered in a kiln. Under an oxygen atmosphere, the temperature is first raised to 600°C at a rate of 4°C / min, and after heat treatment for 1 hour, the temperature is raised to 800°C and sintered for 15 hours. Then the temperature is lowered and cooled, and the mixture is passed through a 400-mesh sieve to obtain the modified material.

[0078] (3) Weigh 0.8% cobalt tetroxide (controlling the amount of cobalt introduced to obtain a mass fraction of 0.8% in the product obtained in step (4)) and 0.8% aluminum citrate (controlling the amount of aluminum introduced to obtain a mass fraction of 0.8% in the product obtained in step (4)), add them to a high-speed mixer for mixing. The mixing speed is 800 rpm, the mixing time is 30 min, and the mixing temperature is 45℃. After mixing, a second mixture is obtained.

[0079] (4) The second mixture is loaded into a sagger and fired in a kiln. Under an oxygen atmosphere, the temperature is raised to 710°C at a rate of 4°C / min. The second firing holding time is 14.23h (calculated according to formula 2). Then, the mixture is cooled and then screened, iron is removed, and packaged to obtain the modified product.

[0080] Comparative Example 1 The only difference from Example 1 is that in step (1) of this comparative example, the aluminum hydroxide doping is changed to 0.30% (which does not satisfy Equation 1).

[0081] In this embodiment, W1 = 0.375W2, which does not satisfy Equation 1.

[0082] Comparative Example 2 The only difference from Example 1 is that in step (1) of this comparative example, the aluminum hydroxide doping is changed to 0.16% (which does not satisfy Equation 1).

[0083] In this embodiment, W1 = 0.2W2, which does not satisfy Equation 1.

[0084] Comparative Example 3 The only difference from Example 1 is that in step (3) of this comparative example, the second sintering temperature is 570°C, and t is also calculated according to Equation 2.

[0085] Comparative Example 4 The only difference from Example 1 is that in step (3) of this comparative example, the second sintering temperature is 720°C, and t is also calculated according to Equation 2.

[0086] Comparative Example 5 The only difference from Example 1 is that in step (3) of this comparative example, the second sintering time is t-1h, that is, the second sintering time is always 1 hour less than the sintering time of Example 1.

[0087] Comparative Example 6 The only difference from Example 1 is that in step (3) of this comparative example, the second sintering time is t+1h, that is, the second sintering time is always 1 hour less than the sintering time of Example 1.

[0088] Experimental Example 1 Electrochemical performance testing: The NCM cathode materials obtained in Examples 1-11 and Comparative Examples 1-6 were used as cathode materials to fabricate coin cells for electrochemical performance testing. The fabrication method is as follows: a. The NCM cathode materials prepared in the examples and comparative examples were stirred in a ratio of cathode material powder: conductive agent (SP): adhesive (PVDF) = 90:5:5 to form a uniformly dispersed cathode slurry. The slurry was then coated, punched, and vacuum dried. A lithium metal sheet was used as the negative electrode material for the counter electrode, and a polypropylene film with micropores was used as the battery separator. Ethylene carbonate (EC) / dimethyl carbonate (DMC) with a solvent volume ratio of 1:1 and 1 mol / L LiPF6 were used as the electrolyte. The batteries were assembled into 2430 button batteries in a glove box filled with dry high-purity argon gas and allowed to stand for 10 h. b. After the button batteries have been allowed to stand, charge and discharge them at an ambient temperature of 25°C, at a voltage of 3.0-4.3V, and at a current rate of 0.1C. Perform electrochemical performance tests on Examples 1-11 and Comparative Examples 1-6. Calculate their initial discharge efficiency, i.e.: Initial efficiency = Initial discharge specific capacity / Initial charge specific capacity × 100%.

[0089] c. At 45°C, charge / discharge at 3.0-4.3V with 1C, and perform cycle performance tests on Examples 1-11 and Comparative Examples 1-6. Calculate the capacity retention rate after 50 cycles using the following formula: Capacity retention rate = Specific capacity at 50th discharge / Specific capacity at first discharge × 100%.

[0090] DSC test: a. Activate the button battery that has been left to stand at an ambient temperature of 25°C by charging and discharging it twice at a rate of 0.2C at 3.0-4.3V, and then fully charge it at 0.2C. After that, disassemble the battery in a glove box with an argon atmosphere, remove the electrode plates, clean the electrode plates with DMC, let them air dry, and scrape off the electrode powder for later use.

[0091] b. Weigh approximately 2-3 mg of the positive electrode powder and place it into an aluminum crucible, then seal it and place it in a differential scanning calorimeter for testing (heating rate 10℃ / min).

[0092] Please refer to Table 1 for specific test data. The performance of the high-nickel ternary cathode materials prepared in the test examples and comparative examples is shown in Table 1.

[0093] Table 1. Performance comparison of high-nickel ternary cathode materials prepared in the examples and comparative examples.

[0094] As shown in Table 1, compared with Example 1, the magnesium acetate additive used in Example 2 was replaced with magnesium fluoride. The specific capacity of the battery in Example 2 was slightly lower, but the cycle and DSC performance were basically the same. This indicates that using magnesium fluoride as the magnesium source may slightly reduce the charge and discharge capacity, while using magnesium acetate can further improve the charge and discharge capacity. Compared to Example 1, Example 3, without the addition of magnesium additive, showed a decrease in discharge capacity, first-time efficiency, and DSC peak temperature, indicating that Mg doping inhibits Li... + / Ni 2+ Mixed arrangement promotes normal lithium ion insertion / extraction and reversible migration, enhances the crystal structure stability of ternary materials, thereby improving capacity, first efficiency and DSC peak temperature.

[0095] In Example 1, the modified product D50 is 10.0-11.0 μm; in Example 4, the first crushed material D50 is 8.0-10.0 μm; and in Example 5, the first crushed material D50 is 11.0-13.0 μm. It can be seen that when the modified product D50 is 8.0-13.0 μm, the material can form an Al gradient doped structure, and the resulting battery has good specific capacity, cycle life, and DSC thermal safety performance.

[0096] In Example 1, 0.8% aluminum citrate was used, while in Examples 6 and 7, 0.57% and 0.67% Al were used, respectively. The resulting batteries exhibited good electrical performance, cycle life, and DSC thermal safety performance. This indicates that under the condition of Equation 1, i.e., 0.247 W2≤W1≤0.354 W2, the uniform diffusion of Al during secondary sintering can facilitate the formation of an Al concentration gradient structure, thereby contributing to improved capacity, cycle life, and thermal safety performance. Compared to Example 1, where the cobalt tetroxide additive was replaced with cobalt hydroxide and no cobalt tetroxide additive was added, Examples 8 and 9 resulted in a decrease in specific capacity and initial efficiency of the batteries, respectively, but both remained at a high level. This indicates that cobalt tetroxide is beneficial for optimizing Li... +The migration channel reduces the interfacial charge transfer impedance, thereby improving the discharge specific capacity. At the same time, Co coating can enhance the structural thermal stability of the material. In addition, the thermal decomposition temperature of cobalt hydroxide coating is relatively low. Under the secondary sintering process, incompletely decomposed hydroxyl groups are easy to remain, which will cause interfacial side reactions during the first charge, consume some active lithium, and result in a higher first irreversible capacity. The actual charge and discharge specific capacity that can be achieved is slightly lower than that of the cobalt oxide coated system. The only difference between Examples 10 and 11 and Example 1 is that the parameter values ​​in steps (1)-(4) are different (the Li / Me, magnesium acetate concentration, mixing parameters, first sintering, and second sintering conditions are changed within a suitable range). The battery specific capacity, cycle life, and DSC thermal safety performance obtained are all good, indicating that the conditions are conducive to the formation of Al gradient doping structure, and a high-capacity, high-cycle life, and high-safety cathode material is successfully obtained.

[0097] In Comparative Examples 1 and 2, step (1) was modified by changing the aluminum hydroxide doping concentration to 0.30% and 0.16% (which does not satisfy Equation 1). This indicates that both excessively high and low aluminum doping concentrations are not conducive to the formation of an Al concentration gradient structure. Excessively high Al doping concentrations tend to form a uniform doping structure, while excessively low Al doping concentrations tend to enrich Al on or near the surface. As a result, the capacity, cycle life, and DSC peak temperature of the obtained battery all decreased significantly. This shows that Equation 1 in this invention defines a specific Al content relationship, and the resulting high-nickel cathode material is conducive to the formation of an Al gradient doping structure, thus successfully obtaining a high-capacity, high-cycle, and safe high-nickel cathode material.

[0098] In step (4) of Example 1, the second sintering temperature is 690℃, while in step (4) of Comparative Examples 3 and 4, the second sintering temperatures are 570℃ and 720℃ respectively (not satisfying the temperature range of T in Formula 2). The resulting battery specific capacity, cycle life, and DSC peak temperature are all poor, indicating that if the second sintering temperature is too low, more Al will accumulate on the surface of the secondary particles, which is not conducive to the formation of an Al concentration gradient. If the second sintering temperature is too high, Al will be more uniformly distributed in the secondary particle bulk phase, which is not conducive to the formation of an Al concentration gradient. Neither of these conditions can effectively improve the electrical performance and thermal safety performance.

[0099] In step (4) of Example 1, the second sintering time was t (13.75h). In step (4) of Comparative Examples 5 and 6, the second sintering times were 12.75h ​​and 14.75h, respectively. The battery specific capacity, cycle life, and DSC peak temperature performance obtained were still poor. This indicates that if the second sintering time is too short, Al cannot diffuse sufficiently from the particle surface, the shallow layer, and then to the inner layer. More Al accumulates on the surface of the secondary particles. If the second sintering time is too long, Al diffuses sufficiently from the outer layer to the inner layer and is distributed more evenly in the secondary particle bulk phase. Neither of these conditions is conducive to the formation of an Al concentration gradient. Therefore, neither of these conditions can effectively improve the electrical performance and thermal safety performance.

[0100] Figure 1 The image shows the overall SEM image of the high-nickel cathode material in Example 1. It can be seen that the high-nickel cathode material of the present invention is a secondary particle formed by primary particle agglomeration.

[0101] Figure 2 , Figure 3 , Figure 4 To fabricate coin cells using the high-nickel cathode materials in Comparative Example 1 and Example 1, the 0.1C first-cycle charge-discharge curve, the 45℃ charge-discharge cycle performance curve, and the obtained DSC spectrum were tested. The figures show that the gradient aluminum-doped modified high-nickel ternary cathode material obtained in this invention has higher specific capacity, cycle life, and a higher DSC peak temperature compared to the unmodified material. In summary, the gradient aluminum-doped modified high-nickel ternary cathode material obtained in this invention achieves bulk lattice stability, surface interface protection, and long-term cycle stability without sacrificing the high specific capacity advantage of high-nickel materials, thus fundamentally solving the structural failure and safety problems of high-nickel ternary cathode materials.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-nickel ternary cathode material, characterized in that, include: The ternary precursor, lithium source and first aluminum source are mixed to obtain the first mixture; The first mixture is sintered once to obtain a modified material; The primary modified material is mixed with a second aluminum source to obtain a second mixture; The second mixture is subjected to secondary sintering to obtain the modified product; Wherein, the mass fraction of aluminum element introduced by the first aluminum source in the modified product is W1, and the mass fraction of aluminum element introduced by the second aluminum source in the modified product is W2, wherein W1 and W2 satisfy: Formula 1; The sintering time t for secondary sintering satisfies: Formula 2; In the formula, the unit of t is h; D 50 The average particle size of the secondary particles in the primary modified material is expressed in μm. d represents the average grain size of the primary particles in the primary modified material, in nm; T represents the sintering temperature of the secondary sintering, in °C.

2. The preparation method according to claim 1, characterized in that, The parameters in Equations 1 and 2 satisfy the following: 0.5%≤W2≤1.2%; 180nm≤d≤350nm; 8.0μm≤D50≤13.0μm; 580℃≤T≤710℃.

3. The preparation method according to claim 1 or 2, characterized in that, The first aluminum source and the second aluminum source are each independently selected from at least one of aluminum hydroxide, aluminum oxide, aluminum phosphate, aluminum sulfate, aluminum oxalate, aluminum acetate and aluminum citrate; Preferably, the first aluminum source is selected from aluminum hydroxide; The second aluminum source is selected from aluminum citrate.

4. The preparation method according to claim 1 or 2, characterized in that, The steps for preparing the first mixture include: mixing the ternary precursor, lithium source, first aluminum source and magnesium source; Preferably, by adjusting the amount of lithium source added, the molar ratio of lithium to the total amount of nickel, cobalt, and manganese in the ternary precursor is 1.04-1.

08. Preferably, the amount of magnesium source is adjusted so that the mass fraction of magnesium in the modified product is 0.05%-0.20%; more preferably, the magnesium source is selected from at least one of magnesium acetate, magnesium oxide, magnesium hydroxide, magnesium sulfate and magnesium carbonate. Preferably, during the preparation of the first mixture, the stirring rate is controlled at 700 rpm-900 rpm, the mixing time is 40 min-60 min, and the mixing temperature is 25℃-45℃.

5. The preparation method according to claim 4, characterized in that, The ternary precursor is nickel cobalt manganese hydroxide with the chemical formula NixCoyMnz(OH)2, 0.80≤x≤0.98, and x+y+z=1.

6. The preparation method according to claim 1 or 2, characterized in that, The steps of a single sintering process include: first holding at 400℃-600℃ for 1h-3h, and then holding at 750℃-800℃ for 10h-15h. Preferably, the heating rate for a single sintering is controlled to be 2℃ / min-4℃ / min; Preferably, the primary sintering is carried out in an oxygen-containing atmosphere, and after sintering, the material is cooled and passed through a 400-mesh sieve to obtain the primary modified material.

7. The preparation method according to claim 1 or 2, characterized in that, The step of preparing the second mixture includes: mixing the primary modified material, the second aluminum source, and the cobalt source; Preferably, the amount of cobalt source added is adjusted so that the mass fraction of cobalt in the modified product is 0.4%-0.8%; Preferably, the cobalt source is selected from at least one of cobalt tetroxide, cobalt hydroxide, cobalt sulfate, cobalt chloride, cobalt carbonate, and cobalt nitrate; Preferably, during the preparation of the second mixture, the stirring rate is controlled at 600 rpm-800 rpm, the mixing time is 30 min-60 min, and the mixing temperature is 25℃-45℃.

8. The preparation method according to claim 1 or 2, characterized in that, Secondary sintering is carried out in an oxygen-containing atmosphere. After sintering, the temperature is lowered and then screened and iron is removed. And / or, control the heating rate of the secondary sintering to be 2℃ / min-4℃ / min.

9. A high-nickel ternary cathode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. A lithium-ion battery, characterized in that, Including the high-nickel ternary cathode material as described in claim 9.

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