Gradient cathode material, preparation method thereof and lithium ion battery

Abstract

The application relates to the field of lithium ion battery materials, and discloses a gradient positive electrode material, a preparation method thereof and a lithium ion battery. The preparation method comprises the following steps: (1) co-precipitating metal salts to obtain a doped gradient precursor; (2) co-pre-sintering the doped gradient precursor and a first lithium source to obtain a lithium-poor oxide; and (3) co-lithium-supplementing two-stage sintering of the lithium-poor oxide and a second lithium source to obtain the gradient positive electrode material; wherein, in the co-precipitation process, a doping element is added twice; the chemical composition of the doped gradient precursor satisfies the chemical formula (Ni x D y M z )(OH)2, the concentration of Ni is gradient-distributed from the core to the surface of the doped gradient precursor, and the difference between the concentrations of Ni at the core and the surface is not less than 15%. The prepared gradient positive electrode material can well retain the concentration gradient characteristics of the precursor, has good thermal stability, excellent high-rate discharge performance and good cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, specifically to a gradient cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the continuous expansion of the global electric vehicle market, the application of lithium-ion batteries in electric vehicles faces a series of new challenges, such as cost, charging behavior, driving range per charge, thermal runaway risk, and battery life. These challenges largely depend on the cathode, which determines the capacity, cycle stability, and thermal behavior of lithium-ion batteries. Therefore, extensive research has been conducted on novel high-performance cathode materials, such as increasing the energy density of nickel-rich layered cathodes by raising the Ni content to over 90%. However, high-nickel cathodes, especially when the Ni content exceeds 90%, exhibit inherent structural instability under deep charge states, leading to rapid capacity decay and high thermal instability.

[0003] To improve the reliability of nickel-rich cathode materials, various methods have been explored to suppress the formation of microcracks in cathode particles. One such method is to introduce a concentration gradient into the cathode particles.

[0004] Transition metal ions, as components of the concentration gradient cathode particles, exhibit different functions depending on their concentration relative to the cathode particle core. Unstable Ni ions concentrate at the core of the cathode particles, conferring high capacity, while Co and Mn ions concentrate on the surface of the cathode particles, mitigating harmful electrolyte corrosion. More importantly, the spherical secondary concentration gradient cathode particles, comprising closely packed and radially oriented rod-shaped primary particles, possess a unique morphology that effectively dissipates structural strain during cycling, limiting microcrack formation and thus improving cycling stability.

[0005] For high-performance concentration gradient cathode materials, establishing a structure that combines morphological features with compositional arrangement within secondary particles is crucial. However, during the high-temperature lithiation process that forms a layered crystal structure, the interdiffusion of TM ions and the resulting coarsening of primary particles inevitably occur, thereby compromising the advantageous properties of concentration gradient cathode materials.

[0006] Therefore, customizing the fine microstructure and controlling the precise lithiation process are crucial for the successful synthesis of high-performance concentration gradient cathode materials. Summary of the Invention

[0007] This invention addresses the problems of rapid diffusion of transition metals in the cathode material, coarsening of primary cathode material particles, and brittleness of cathode material particles in existing high-nickel gradient cathode material preparation methods, which in turn affect the thermal stability, high-rate discharge performance, and cycle stability of high-nickel gradient cathode materials. The invention provides a gradient cathode material, its preparation method, and a lithium-ion battery.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a gradient cathode material, comprising:

[0009] (1) Co-precipitate the metal salt to obtain the doped gradient precursor;

[0010] (2) The doped gradient precursor and the first lithium source are pre-sintered together to obtain lithium-poor oxide;

[0011] (3) The lithium-poor oxide and the second lithium source are subjected to a two-stage sintering process to obtain a gradient cathode material;

[0012] In the co-precipitation process, the dopant element is added in two stages;

[0013] The chemical composition of the doped gradient precursor satisfies the chemical formula (Ni x D y M z (OH)2, wherein element D is selected from at least one of Mn, Co, Al, Zr, Ti and Mg;

[0014] The oxide of doped element M satisfies the chemical formula M a O b Where a and b are positive integers, and b / a > 1.5;

[0015] 0.8≤x<1, x+y=1, 0.0002≤z≤0.02;

[0016] In the doped gradient precursor, the Ni concentration is distributed in a gradient from the core to the surface of the doped gradient precursor and gradually decreases, and the Ni concentration difference between the core and the surface is not less than 15%.

[0017] The second aspect of the present invention provides a gradient cathode material prepared by the method described in the first aspect above.

[0018] A third aspect of the present invention provides a lithium-ion battery comprising the gradient cathode material described in the second aspect above.

[0019] The method for preparing gradient cathode materials provided by this invention involves doping specific metal elements twice during the co-precipitation preparation of the precursor, and then performing a two-stage sintering process of pre-sintering and lithium supplementation on the resulting doped gradient precursor. This allows the prepared gradient cathode material to retain the concentration gradient characteristics of the precursor well, overcoming the disadvantages of high-nickel cathode materials such as brittle particles and poor processing. It features good thermal stability, excellent high-rate discharge performance, and good cycle stability, and can better meet the performance requirements of lithium-ion battery cathode materials in the power and power tool markets. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0021] Figure 1 This is a scanning electron microscope image of the cathode material prepared in Example 1.

[0022] Figure 2 This is a scanning electron microscope image of the cathode material prepared in Comparative Example 1. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The first aspect of this invention provides a method for preparing a gradient cathode material, comprising:

[0025] (1) Co-precipitate the metal salt to obtain the doped gradient precursor;

[0026] (2) The doped gradient precursor and the first lithium source are pre-sintered together to obtain lithium-poor oxide;

[0027] (3) The lithium-poor oxide and the second lithium source are subjected to a two-stage sintering process to obtain a gradient cathode material;

[0028] In the co-precipitation process, the dopant element is added in two stages;

[0029] The chemical composition of the doped gradient precursor satisfies the chemical formula (Ni x D y M z(OH)2, wherein element D is selected from at least one of Mn, Co, Al, Zr, Ti and Mg;

[0030] The oxide of doped element M satisfies the chemical formula M a O b Where a and b are positive integers, and b / a > 1.5;

[0031] 0.8≤x<1, x+y=1, 0.0002≤z≤0.02;

[0032] In the doped gradient precursor, the Ni concentration decreases gradually from the core to the surface of the doped gradient precursor, and the Ni concentration difference (mol%) between the core and the surface is not less than 15%.

[0033] According to the present invention, in the preparation method of the gradient cathode material, in step (1), the chemical composition of the doped gradient precursor satisfies the chemical formula (Ni x D y M z (OH)2, wherein, preferably, element D can be selected from at least one of Mn, Co and Al, which can obtain a better layered structure of the cathode material.

[0034] According to the present invention, the dopant element M is a metallic element, and the dopant element M can be one element or multiple elements. In addition to satisfying the above-mentioned oxide composition, the dopant element M is preferably selected from at least one of W, Mo, Ti, Nb, and Sb, which can increase the diffusion barrier energy of transition metal ions inside the material during sintering, reduce interdiffusion, better maintain gradient characteristics, and minimize grain coarsening through grain boundary pinning effect, thereby improving rate performance.

[0035] According to the present invention, in the preparation method of the gradient cathode material, the method and parameters for the coprecipitation in step (1) are more limited, and the method and parameters for preparing the gradient precursor by coprecipitation reaction of metal salt in alkaline solution, which are known in the art, can be used.

[0036] According to the present invention, preferably, in the doped gradient precursor, the Ni concentration difference between the core and the surface is 15-65%.

[0037] According to the present invention, in the method for preparing the gradient cathode material, step (1), the addition of doping elements in two stages includes:

[0038] When the precursor obtained by co-precipitation grows to D50 of r1, a first compound containing doped element M is added; wherein, r1 / R = (30-50):100;

[0039] When the precursor obtained by co-precipitation grows to D50 of r2, a second compound containing doped element M is added; wherein, r2 / R = (60-80):100;

[0040] Wherein, R is the D50 value of the doped gradient precursor.

[0041] In this invention, the "precursor obtained by coprecipitation" refers to the precipitate product generated during the coprecipitation reaction of metal salt raw materials. The precipitate product gradually grows during the coprecipitation reaction, and doping elements are added twice during the growth process to finally form the doped gradient precursor.

[0042] According to the present invention, in the preparation method of the gradient cathode material, by adding the dopant element in two stages in the co-precipitation process in the manner described above, the dopant element can be uniformly distributed in the material through diffusion during the sintering process, effectively avoiding element segregation and enrichment on the particle surface.

[0043] According to the present invention, in the method for preparing the gradient cathode material, preferably, the D50 of the doped gradient precursor is 3-20 μm, which is beneficial for the secondary particles to obtain good sphericity and for the primary particles of the gradient material to have good uniformity.

[0044] In this invention, the D50 of the particles can be determined by a laser particle size analyzer.

[0045] According to the present invention, in the preparation method of the gradient cathode material, in step (1), preferably, the feeding amounts of the first compound and the second compound satisfy the relationship: 0 < (r1) 3 / R 3 ) / (n1 / n1+n2)≤1;

[0046] Wherein, n1 is the amount of the first compound fed (in terms of substance) based on doping element M, and n2 is the amount of the second compound fed (in terms of substance) based on doping element M.

[0047] According to the present invention, in the preparation method of the gradient cathode material, during the co-precipitation process, by controlling the amount of the first compound and the second compound to satisfy the above-mentioned relationship, the dopant elements can be reasonably distributed at different positions in the precursor according to the design amount, which is beneficial to increase the diffusion barrier energy of the transition metal ions inside the material during sintering and reduce mutual diffusion.

[0048] According to the present invention, the total amount of the first compound and the second compound is such that the chemical composition of the resulting doped gradient precursor satisfies the chemical formula (Ni). x D y M z(OH)2, wherein element D is selected from at least one of Mn, Co, Al, Zr, Ti, and Mg; the oxide of doped element M satisfies the chemical formula M a O b Where a and b are positive integers, b / a > 1.5; 0.8 ≤ x < 1, x + y = 1, 0.0002 ≤ z ≤ 0.02.

[0049] According to the present invention, the first compound and the second compound are soluble in water and can react in an alkaline solution to form a precipitate. Preferably, the first compound and the second compound are selected from at least one of nitrates, sulfates, chlorides, and phosphates doped with element M.

[0050] In this invention, the types of dopant elements M contained in the first compound and the second compound may be the same or different.

[0051] According to a preferred embodiment of the present invention, in the preparation method of the gradient cathode material, in step (1), nickel salt, salt containing element D and water are respectively prepared into mixed solution A (Ni: element D molar ratio of 5-49:1) and mixed solution B (Ni: element D molar ratio of 0.5-2.3:1). Under N2 atmosphere, mixed solution A is first placed in a reactor, and then mixed solution B is continuously added to the reactor. At the same time, ammonia water and NaOH solution are added to the reactor to carry out co-precipitation reaction. When the precursor obtained by co-precipitation grows to D50 of r1 (r1 / R = 30-50:100), a first compound containing doped element M is added. When the precursor obtained by co-precipitation grows to D50 of r2 (r2 / R = 60-80:100), a second compound containing doped element M is added. The amount of the first compound and the second compound fed satisfies the relationship: 0 < (r1 / R = 30-50:100). 3 / R 3 ) / (n1 / n1+n2)≤1 (n1 is the amount of the first compound fed in terms of doping element M, and n2 is the amount of the second compound fed in terms of doping element M); the temperature of the coprecipitation reaction is 40-80℃, the stirring rate is 200-1000 rpm, and the pH value of the reaction system is 10.5-13.5; after the reaction, the obtained product system is subjected to solid-liquid separation, washing, drying and sieving in sequence to obtain the doped gradient precursor.

[0052] According to the present invention, in the preparation method of the gradient cathode material, in step (2), the doped gradient precursor is pre-oxidized and more lithium vacancies are generated through the pre-sintering, which is beneficial to the subsequent two-stage lithium supplementation sintering to further improve the crystal structure and reduce the degree of cation mixing. Preferably, the weight ratio of the first lithium source to the doped gradient precursor is (0.355-0.456):1.

[0053] According to the present invention, in the preparation method of the gradient cathode material, the pre-sintering conditions in step (2) include: a heating rate of 3-6℃ / min, a sintering temperature of 300-650℃, and a sintering time of 3-10h.

[0054] According to the present invention, the sintering atmosphere for pre-sintering can be one of an air atmosphere, a mixture of air and oxygen, or an oxygen atmosphere. Preferably, the volume concentration of oxygen in the sintering atmosphere for pre-sintering is 20-50%.

[0055] According to the present invention, preferably, during the pre-sintering process, the pressure difference between the internal and external gas pressure of the kiln is not greater than 0 Pa, and more preferably -9 to 0 Pa.

[0056] According to the present invention, in the method for preparing the gradient cathode material, in step (2), preferably, the D50 of the first lithium source is 200-500 μm. Using a first lithium source that meets the above particle size is beneficial for controlling the thermodynamic reaction rate of lithium ions, generating more lithium vacancies, and reducing production costs.

[0057] According to the present invention, in the preparation method of the gradient cathode material, in step (2), the lithium-poor oxide is subjected to XRD testing, and the lithium-poor oxide has an I 003 / I 104 The peak intensity ratio is 0.5-1.5, indicating that lithium and oxygen increase, lithium and transition metals become more ordered, forming a layered structure R-3m.

[0058] According to the present invention, in the preparation method of the gradient cathode material, in step (3), preferably, the weight ratio of the second lithium source to lithium-poor oxide is (0.001-0.131):1.

[0059] According to the present invention, in the preparation method of the gradient cathode material, in step (3), preferably, the D50 of the second lithium source is 5-30 μm. Using a second lithium source that meets the above particle size facilitates lithium ions entering lithium vacancies for lithium replenishment under lower temperature conditions.

[0060] According to the present invention, preferably, the weight ratio of the first lithium source to the doped gradient precursor and the weight ratio of the second lithium source to the lithium-poor oxide satisfy the following relationship: 0.444 < Q1 + Q2 ≤ 0.493; where Q1 is the weight ratio of the first lithium source to the doped gradient precursor and Q2 is the weight ratio of the second lithium source to the lithium-poor oxide. By satisfying the above quantitative relationship, the total proportion of lithium salt can be controlled, avoiding insufficient or excessive lithium from affecting product performance.

[0061] According to the present invention, in the preparation method of the gradient cathode material, step (3) involves a two-stage lithium-filling sintering process, which is divided into a first-stage sintering and a second-stage sintering performed sequentially. During the first-stage sintering, lithium vacancy replenishment is performed at a relatively low sintering temperature, followed by a slow temperature rise to initiate the second-stage sintering. This allows the metal ions to undergo a full solid-phase reaction, effectively reducing anti-site defects. Finally, a short-duration isothermal sintering enhances the microstructure of the sintered product. By employing this two-stage lithium-filling sintering, structural defects such as cation mixing caused by traditional one-stage and two-stage sintering can be effectively reduced, as well as gradient weakening and subsequent coarsening of primary particles caused by rapid diffusion of transition metals.

[0062] According to the present invention, preferably, the conditions for the first sintering stage include: a heating rate of 5-8°C / min, a sintering temperature of 350-750°C, and a sintering time of 3-10h.

[0063] According to the present invention, preferably, the sintering temperature of the first sintering stage is 50-100°C higher than the sintering temperature of the pre-sintering stage, which is more conducive to lithium ions preferentially entering lithium vacancies for lithium replenishment.

[0064] According to the present invention, preferably, the conditions for the second stage of sintering include: a heating rate of 0.05-0.5℃ / min, a sintering temperature of 600-900℃, and a sintering time of 2-5h.

[0065] According to the present invention, in the method for preparing the gradient cathode material, in step (3), the sintering atmosphere for the two-stage lithium supplementation sintering can be an oxygen atmosphere or a mixture of air and oxygen. Preferably, the volume concentration of oxygen in the sintering atmosphere for the two-stage lithium supplementation sintering is not less than 90%.

[0066] According to the present invention, preferably, during the two-stage lithium supplementation sintering process, the pressure difference between the internal gas pressure and the external gas pressure of the kiln is not less than 0 Pa, and more preferably 0 to 9 Pa.

[0067] In this invention, preferably, the temperatures of the first sintering stage in the pre-sintering and lithium replenishment two-stage sintering and the second sintering stage in the lithium replenishment two-stage sintering are increased sequentially.

[0068] In this invention, the first lithium source and the second lithium source can be any lithium source conventionally used in the preparation of cathode materials in the art. Preferably, the first lithium source and the second lithium source are lithium hydroxide.

[0069] The method for preparing gradient cathode materials provided by this invention involves two separate additions of specific metal elements during the co-precipitation preparation of the precursor. This increases the diffusion barrier energy of transition metal ions within the material during subsequent sintering, reduces inter-diffusion, and effectively suppresses grain coarsening through grain boundary pinning. Furthermore, the lithiation process is precisely controlled. The doped gradient precursor is pre-sintered to generate more lithium vacancies, followed by a two-stage lithium-filling sintering process. This effectively reduces structural defects such as cation mixing caused by traditional one-stage and two-stage sintering, as well as gradient weakening and subsequent primary particle coarsening resulting from rapid transition metal diffusion. The gradient cathode material prepared using this method retains the concentration gradient characteristics of the precursor well, overcomes the shortcomings of high-nickel cathode materials such as brittle particles and poor processing, and exhibits good thermal stability, excellent high-rate discharge performance, and good cycle stability.

[0070] The second aspect of the present invention provides a gradient cathode material prepared by the method described in the first aspect above.

[0071] The gradient cathode material provided by this invention is a lithium-containing metal oxide compound with a layered structure, and the chemical composition of the gradient cathode material satisfies the chemical formula LiNi. x D y M z O, wherein element D is selected from at least one of Mn, Co, Al, Zr, Ti and Mg;

[0072] The oxide of doped element M satisfies the chemical formula M a O b Where a and b are positive integers, and b / a > 1.5;

[0073] 0.8≤x<1, x+y=1, 0.0002≤z≤0.02;

[0074] In the gradient cathode material, the Ni concentration is distributed in a gradient from the core to the surface and gradually decreases, and the Ni concentration difference (mol%) between the core and the surface is not less than 10%, preferably 10-60%.

[0075] According to the present invention, the D50 of the gradient cathode material is 3-20 μm.

[0076] According to the present invention, the D90, D50 and D10 of the gradient cathode material satisfy: 0.3≤(D90-D10) / D50≤1.5.

[0077] In this invention, the D90, D50, and D10 of the particles can be measured using a laser particle size analyzer.

[0078] According to the present invention, the minor axis diameter of the primary particles of the gradient cathode material is 150-500 nm.

[0079] According to the present invention, the ratio of the minor axis diameter of the primary particles to the D50 of the secondary particles of the gradient cathode material is 0.0075-0.17.

[0080] In this invention, the minor axis diameter of the primary particles of the gradient cathode material is determined by the following method: the scanning electron microscope (SEM) test results of the cathode material are imported into Nano Measurer software, the minor axis diameter of the primary particles of the cathode material in the SEM test results is measured one by one by Nano Measurer software, and the average minor axis diameter of the primary particles of the gradient cathode material is obtained by statistical analysis using the software.

[0081] The gradient cathode material provided by this invention can effectively retain the concentration gradient of the precursor, effectively suppress the coarsening of primary particles, and has fewer structural defects. It features good thermal stability, excellent high-rate discharge performance, and good cycle stability, thereby improving the electrical performance of lithium-ion batteries.

[0082] A third aspect of the present invention provides a lithium-ion battery comprising the gradient cathode material described in the second aspect above.

[0083] The lithium-ion battery provided by this invention uses a gradient cathode material prepared by the method provided by this invention, and has excellent high-rate discharge performance and cycle stability.

[0084] The present invention will be described in detail below through examples. Unless otherwise specified, the following examples and comparative examples are all conventional methods; the reagents and materials mentioned are commercially available unless otherwise specified.

[0085] Example 1

[0086] The target gradient cathode material prepared in this embodiment has a chemical composition that satisfies the chemical formula LiNi. 0.90 Co 0.05 Mn 0.05 W 0.001 O2, the D50 (i.e. R) of this gradient cathode material is 12.0 μm.

[0087] (1) Prepare mixed solution A (in mixed solution A, the molar ratio of Ni:(Co+Mn) is 49:1) and mixed solution B (in mixed solution B, the molar ratio of Ni:(Co+Mn) is 0.5:1) by mixing nickel sulfate, cobalt sulfate, manganese sulfate and water respectively; under N2 atmosphere, first place the above mixed solution A in the reactor, and then continuously add the above mixed solution B to the reactor, while adding ammonia water and NaOH solution to the reactor respectively to carry out co-precipitation reaction;

[0088] When the precursor obtained from the coprecipitation reaction grows to a D50 of 5.5 μm (i.e., r1 = 5.5 μm, r1 / R = 42:100), tungsten nitrate (the first compound) is added; when the precursor obtained from the coprecipitation reaction grows to a D50 of 9.2 μm (i.e., r2 = 9.2 μm, r2 / R = 71:100), tungsten nitrate (the second compound) is added; wherein the amounts of the first and second compounds fed satisfy the following relationship: (r1 3 / R 3 ) / (n1 / n1+n2)=0.12 (where n1 is the amount of the first compound fed in terms of doping element W, and n2 is the amount of the second compound fed in terms of doping element W);

[0089] The coprecipitation reaction was carried out at a temperature of 65℃, a stirring rate of 500 rpm, and a pH of 11.2. After the reaction, the resulting product system was subjected to solid-liquid separation, washing, drying, and sieving to obtain the doped gradient precursor (denoted as M1).

[0090] The chemical composition of M1 satisfies the chemical formula (Ni 0.90 Co 0.05 Mn 0.05 W 0.001 (OH)2, the D50 of M1 is 13.0 μm;

[0091] The elemental composition at different locations along the M1 profile was determined by energy dispersive X-ray spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in M1, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 64.8%.

[0092] (2) Lithium hydroxide (D50 is 350μm) and the above-mentioned doped gradient precursor M1 are mixed evenly in a high-speed mixer at a weight ratio of 0.405:1 (i.e. Q1). The resulting mixture is loaded into a sagger and transferred to a kiln with an air atmosphere (oxygen volume concentration of 40%) for pre-sintering. The pressure difference between the internal and external air pressure of the kiln is -5±1Pa. The temperature is raised to 560℃ at a heating rate of 4℃ / min and the constant temperature sintering time is 8h. The sintered product is naturally cooled to room temperature in air to obtain lithium-poor oxide.

[0093] XRD analysis was performed on the aforementioned lithium-poor oxide, and the peak intensity ratio (i.e., I0) between the first characteristic peak (around 2θ = 18.6°) and the fourth characteristic peak (around 2θ = 44.3°) was calculated. 003 / I104 The value is 0.88;

[0094] (3) Lithium hydroxide (D50 is 11.0 μm) and the above-mentioned lithium-poor oxide are mixed evenly in a high-speed mixer at a weight ratio of 0.061:1 (i.e., Q2). The resulting mixture is loaded into a sagger and transferred to a kiln with a mixed atmosphere of air and oxygen (oxygen volume concentration is 95%) for lithium supplementation and two-stage sintering. The pressure difference between the internal and external air pressure of the kiln is 3±1 Pa. The temperature is first raised to 650℃ at a heating rate of 6℃ / min and sintered at a constant temperature for 5 hours. Then, the temperature is raised to 760℃ at a heating rate of 0.1℃ / min and sintered at a constant temperature for 3 hours. The sintered product is naturally cooled to room temperature and then pulverized to obtain a gradient cathode material (denoted as P1).

[0095] P1 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of P1 satisfies the chemical formula LiNi. 0.90 Co 0.05 Mn 0.05 W 0.001 O2;

[0096] P1 has a D90 of 14.8 μm, a D50 of 12.0 μm, a D10 of 9.9 μm, and a (D90-D10) / D50 ratio of 0.41.

[0097] A scanning electrical test was performed on P1, and the results are as follows: Figure 1 As shown, Figure 1 The primary particles of the gradient cathode material are fine and uniform, and no particle coarsening has occurred.

[0098] The minor axis diameter of the primary particle of P1 is 310 nm; the ratio of the minor axis diameter of the primary particle of P1 to the D50 of the secondary particle is 0.026.

[0099] The elemental composition at different locations in the P1 profile was determined by X-ray energy dispersive spectroscopy (EDS) (results are shown in Table 1). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in P1, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 42.1%.

[0100] Example 2

[0101] The target gradient cathode material prepared in this embodiment has a chemical composition that satisfies the chemical formula LiNi. 0.88 Co 0.07 Mn 0.05 Mo 0.0008 Nb 0.0002O2, the D50 (i.e., R) of this gradient cathode material is 10.0 μm.

[0102] (1) Prepare mixed solution A (in mixed solution A, the molar ratio of Ni:(Co+Mn) is 13.3:1) and mixed solution B (in mixed solution B, the molar ratio of Ni:(Co+Mn) is 1:1) by mixing nickel sulfate, cobalt sulfate, manganese sulfate and water respectively; under N2 atmosphere, first place the above mixed solution A in the reactor, and then continuously add the above mixed solution B to the reactor, while adding ammonia water and NaOH solution to the reactor respectively to carry out co-precipitation reaction;

[0103] When the precursor obtained from the coprecipitation reaction grows to a D50 of 3.3 μm (i.e., r1 = 3.3 μm, r1 / R = 31:100), molybdenum nitrate (the first compound) is added; when the precursor obtained from the coprecipitation reaction grows to a D50 of 6.5 μm (i.e., r2 = 6.5 μm, r2 / R = 60:100), niobium nitrate (the second compound) is added; wherein the amounts of the first and second compounds fed satisfy the following relationship: (r1 3 / R 3 ) / (n1 / n1+n2)=0.035 (where n1 is the amount of the first compound fed in terms of doping element Mo, and n2 is the amount of the second compound fed in terms of doping element Nb);

[0104] The coprecipitation reaction was carried out at a temperature of 58℃, a stirring rate of 500 rpm, and a pH of 11.5. After the reaction, the resulting product system was subjected to solid-liquid separation, washing, drying, and sieving to obtain the doped gradient precursor (denoted as M2).

[0105] The chemical composition of M2 satisfies the chemical formula (Ni 0.88 Co 0.07 Mn 0.05 Mo 0.0008 Nb 0.0002 (OH)2, the D50 of M2 is 10.8 μm;

[0106] The elemental composition at different locations along the M2 profile was determined by energy dispersive X-ray spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in M2, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 43.1%.

[0107] (2) Lithium hydroxide (D50 is 350μm) and the above-mentioned doped gradient precursor M2 are mixed evenly in a high-speed mixer at a weight ratio of 0.405:1 (i.e. Q1). The resulting mixture is loaded into a sagger and transferred to a kiln with an air atmosphere (oxygen volume concentration of 40%) for pre-sintering. The pressure difference between the internal and external air pressure of the kiln is -5±1Pa. The temperature is raised to 560℃ at a heating rate of 4℃ / min and the constant temperature sintering time is 8h. The sintered product is naturally cooled to room temperature in air to obtain lithium-poor oxide.

[0108] XRD analysis was performed on the aforementioned lithium-poor oxide, and the peak intensity ratio (i.e., I0) between the first characteristic peak (around 2θ = 18.6°) and the fourth characteristic peak (around 2θ = 44.3°) was calculated. 003 / I 104 The value is 0.93;

[0109] (3) Lithium hydroxide (D50 is 11.0 μm) and the above-mentioned lithium-poor oxide are mixed evenly in a high-speed mixer at a weight ratio of 0.061:1 (i.e., Q2). The resulting mixture is loaded into a sagger and transferred to a kiln with a mixed atmosphere of air and oxygen (oxygen volume concentration is 95%) for lithium supplementation and two-stage sintering. The pressure difference between the internal and external air pressure of the kiln is 3±1 Pa. First, the temperature is raised to 650℃ at a heating rate of 6℃ / min and sintered at a constant temperature for 5 hours. Then, the temperature is raised to 755℃ at a heating rate of 0.15℃ / min and sintered at a constant temperature for 3 hours. The sintered product is naturally cooled to room temperature and then pulverized to obtain a gradient cathode material (denoted as P2).

[0110] P2 is a lithium-containing metal oxide compound with a layered structure, while the chemical composition of P1 satisfies the chemical formula LiNi. 0.88 Co 0.07 Mn 0.05 Mo 0.0008 Nb 0.0002 O2;

[0111] P2 has a D90 of 11.6 μm, a D50 of 10.0 μm, a D10 of 8.7 μm, and a (D90-D10) / D50 ratio of 0.3.

[0112] The minor axis diameter of the primary particles of P2 is 370 nm; the ratio of the minor axis diameter of the primary particles of P2 to the D50 of the secondary particles is 0.037.

[0113] The elemental composition at different locations in the P2 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2It was found that in P2, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 27.7%.

[0114] Example 3

[0115] The target gradient cathode material prepared in this embodiment has a chemical composition that satisfies the chemical formula LiNi. 0.92 Co 0.05 Mn 0.02 Al 0.01 Zr 0.003 O2, the D50 (i.e., R) of this gradient cathode material is 10.0 μm.

[0116] (1) Prepare mixed solution A (in mixed solution A, the molar ratio of Ni to (Co+Mn+Al) is 24:1) and mixed solution B (in mixed solution B, the molar ratio of Ni to (Co+Mn+Al) is 1.5:1) by mixing nickel sulfate, cobalt sulfate, manganese sulfate, aluminum nitrate and water respectively; under N2 atmosphere, first place the above mixed solution A in the reactor, and then continuously add the above mixed solution B to the reactor, while adding ammonia water and NaOH solution to the reactor respectively to carry out co-precipitation reaction;

[0117] When the precursor obtained from the coprecipitation reaction grows to a D50 of 3.3 μm (i.e., r1 = 3.3 μm, r1 / R = 31:100), zirconium sulfate (the first compound) is added; when the precursor obtained from the coprecipitation reaction grows to a D50 of 6.5 μm (i.e., r2 = 6.5 μm, r2 / R = 60:100), zirconium sulfate (the second compound) is added; wherein the amounts of the first and second compounds fed satisfy the following relationship: (r1 3 / R 3 ) / (n1 / n1+n2)=0.35 (where n1 is the amount of the first compound fed in terms of doping element Zr, and n2 is the amount of the second compound fed in terms of doping element Zr);

[0118] The coprecipitation reaction was carried out at a temperature of 70℃, a stirring rate of 850 rpm, and a pH of 11.8. After the reaction, the resulting product system was subjected to solid-liquid separation, washing, drying, and sieving to obtain the doped gradient precursor (denoted as M3).

[0119] The chemical composition of M3 satisfies the chemical formula (Ni 0.92 Co 0.05 Mn 0.02 Al 0.01 Zr 0.003 The D50 of M3 is 10.8 μm for )(OH)2.

[0120] The elemental composition at different locations in the M3 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in M3, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 36.3%.

[0121] (2) Lithium hydroxide (D50 is 350μm) and the above-mentioned doped gradient precursor M3 are mixed evenly in a high-speed mixer at a weight ratio of 0.422:1 (i.e. Q1). The resulting mixture is loaded into a sagger and transferred to a kiln with an air atmosphere (oxygen volume concentration of 40%) for pre-sintering. The pressure difference between the internal and external air pressure of the kiln is -5±1Pa. The temperature is raised to 500℃ at a heating rate of 4℃ / min and the constant temperature sintering time is 8h. The sintered product is naturally cooled to room temperature in air to obtain lithium-poor oxide.

[0122] XRD analysis was performed on the aforementioned lithium-poor oxide, and the peak intensity ratio (i.e., I0) between the first characteristic peak (around 2θ = 18.6°) and the fourth characteristic peak (around 2θ = 44.3°) was calculated. 003 / I 104 The value is 1.02;

[0123] (3) Lithium hydroxide (D50 is 11 μm) and the above-mentioned lithium-poor oxide are mixed evenly in a high-speed mixer at a weight ratio of 0.038:1 (i.e., Q2). The resulting mixture is loaded into a sagger and transferred to a kiln with a mixed atmosphere of air and oxygen (oxygen volume concentration is 95%) for lithium supplementation and two-stage sintering. The pressure difference between the internal and external air pressure of the kiln is 3±1 Pa. The temperature is first raised to 650℃ at a heating rate of 6℃ / min and sintered at a constant temperature for 5 hours. Then the temperature is raised to 745℃ at a heating rate of 0.2℃ / min and sintered at a constant temperature for 3 hours. The sintered product is naturally cooled to room temperature and then pulverized to obtain a gradient cathode material (denoted as P3).

[0124] P3 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of P3 satisfies the chemical formula LiNi. 0.92 Co 0.05 Mn 0.02 Al 0.01 Zr 0.003 O2;

[0125] P3 has a D90 of 18.9 μm, a D50 of 10.0 μm, a D10 of 5.3 μm, and a (D90-D10) / D50 ratio of 1.4.

[0126] The minor axis diameter of the primary particles of P3 is 240 nm; the ratio of the minor axis diameter of the primary particles of P3 to the D50 of the secondary particles is 0.024.

[0127] The elemental composition at different locations in the P3 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in P3, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 20.4%.

[0128] Example 4

[0129] The target gradient cathode material prepared in this embodiment has a chemical composition that satisfies the chemical formula LiNi. 0.90 Co 0.06 Mn 0.02 Al 0.02 Zr 0.002 Ce 0.001 O2, the D50 (i.e. R) of this gradient cathode material is 13.5 μm.

[0130] (1) Nickel sulfate, cobalt sulfate, manganese sulfate, aluminum nitrate, and water were respectively prepared into mixed solution A (in mixed solution A, the molar ratio of Ni:(Co+Mn+Al) was 49:1) and mixed solution B (in mixed solution B, the molar ratio of Ni:(Co+Mn+Al) was 1.5:1); under N2 atmosphere, the above mixed solution A was first placed in the reactor, and then the above mixed solution B was continuously added to the reactor. At the same time, ammonia water and NaOH solution were added to the reactor to carry out co-precipitation reaction.

[0131] When the precursor obtained from the coprecipitation reaction grows to a D50 of 6.5 μm (i.e., r1 = 6.5 μm, r1 / R = 45:100), zirconium sulfate (the first compound) is added; when the precursor obtained from the coprecipitation reaction grows to a D50 of 10.9 μm (i.e., r2 = 10.9 μm, r2 / R = 75:100), cerium nitrate (the second compound) is added; wherein the amounts of the first and second compounds fed satisfy the following relationship: (r1 3 / R 3 ) / (n1 / n1+n2)=0.135 (where n1 is the amount of the first compound fed in terms of doping element Zr, and n2 is the amount of the second compound fed in terms of doping element Ce);

[0132] The coprecipitation reaction was carried out at a temperature of 63℃, a stirring rate of 750 rpm, and a pH of 11.9. After the reaction, the resulting product system was subjected to solid-liquid separation, washing, drying, and sieving to obtain the doped gradient precursor (denoted as M4).

[0133] The chemical composition of M4 satisfies the chemical formula (Ni 0.90 Co 0.06 Mn 0.02 Al 0.02 Zr 0.002 Ce 0.001 (OH)2, the D50 of M4 is 14.5 μm;

[0134] The elemental composition at different locations on the M4 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in M4, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 36.2%.

[0135] (2) Lithium hydroxide (D50 is 350μm) and the above-mentioned doped gradient precursor M4 are mixed evenly in a high-speed mixer at a weight ratio of 0.392:1 (i.e. Q1). The resulting mixture is loaded into a sagger and transferred to a kiln with an air atmosphere (oxygen volume concentration of 40%) for pre-sintering. The pressure difference between the internal and external air pressure of the kiln is -5±1Pa. The temperature is raised to 480℃ at a heating rate of 4℃ / min and the constant temperature sintering time is 8h. The sintered product is naturally cooled to room temperature in air to obtain lithium-poor oxide.

[0136] XRD analysis was performed on the aforementioned lithium-poor oxide, and the peak intensity ratio (i.e., I0) between the first characteristic peak (around 2θ = 18.6°) and the fourth characteristic peak (around 2θ = 44.3°) was calculated. 003 / I 104 The value is 0.83;

[0137] (3) Lithium hydroxide (D50 is 11 μm) and the above-mentioned lithium-poor oxide are mixed evenly in a high-speed mixer at a weight ratio of 0.080:1 (i.e., Q2). The resulting mixture is loaded into a sagger and transferred to a kiln with a mixed atmosphere of air and oxygen (oxygen volume concentration is 95%) for lithium supplementation and two-stage sintering. The pressure difference between the internal and external air pressure of the kiln is 3±1 Pa. First, the temperature is raised to 680℃ at a heating rate of 6℃ / min and sintered at a constant temperature for 5 hours. Then, the temperature is raised to 755℃ at a heating rate of 0.1℃ / min and sintered at a constant temperature for 3 hours. The sintered product is naturally cooled to room temperature and then pulverized to obtain a gradient cathode material (denoted as P4).

[0138] P4 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of P4 satisfies the chemical formula LiNi. 0.90 Co 0.06 Mn 0.02 Al 0.02 Zr 0.002 Ce 0.001 O2;

[0139] P4 has a D90 of 20.7 μm, a D50 of 13.5 μm, a D10 of 9.2 μm, and a (D90-D10) / D50 ratio of 0.85.

[0140] The minor axis diameter of the primary particles of P4 is 350 nm; the ratio of the minor axis diameter of the primary particles of P4 to the D50 of the secondary particles is 0.026.

[0141] The elemental composition at different locations on the P4 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in P4, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 18.5%.

[0142] Example 5

[0143] The method according to Example 4 differs in that, in step (1), when the precursor obtained from the coprecipitation reaction grows to a D50 of 4.4 μm (i.e., r1 = 4.4 μm, r1 / R = 30:100), zirconium sulfate (first compound) is added; when the precursor obtained from the coprecipitation reaction grows to a D50 of 11.6 μm (i.e., r2 = 11.6 μm, r2 / R = 80:100), cerium nitrate (second compound) is added; wherein, the amounts of the first compound and the second compound fed satisfy the following relationship: (r1 3 / R 3 ) / (n1 / n1+n2)=0.042 (where n1 is the amount of the first compound fed as dopant element Zr, and n2 is the amount of the second compound fed as dopant element Ce). Other steps and conditions are the same as in Example 4, and a gradient cathode material (denoted as P5) is prepared.

[0144] P5 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of P5 satisfies the chemical formula LiNi. 0.90 Co 0.06 Mn 0.02 Al 0.02 Zr 0.002 Ce 0.001 O2;

[0145] P5 has a D90 of 20.7 μm, a D50 of 13.5 μm, a D10 of 9.2 μm, and a (D90-D10) / D50 ratio of 0.85.

[0146] The minor axis diameter of the primary particles of P5 is 370 nm; the ratio of the minor axis diameter of the primary particles of P5 to the D50 of the secondary particles is 0.027.

[0147] The elemental composition at different locations on the P5 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in P5, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 12.3%.

[0148] Example 6

[0149] The method of Example 4 was followed, except that in step (2), during the pre-sintering process, the temperature was increased to 400°C at a heating rate of 6°C / min, and the isothermal sintering time was 10h. Other steps and conditions were the same as in Example 4, and a gradient cathode material (denoted as P6) was prepared.

[0150] P6 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of P6 satisfies the chemical formula LiNi. 0.90 Co 0.06 Mn 0.02 Al 0.02 Zr 0.002 Ce 0.001 O2;

[0151] P6 has a D90 of 20.7 μm, a D50 of 13.6 μm, a D10 of 9.2 μm, and a (D90-D10) / D50 ratio of 0.85.

[0152] The minor axis diameter of the primary particles of P6 is 430 nm; the ratio of the minor axis diameter of the primary particles of P6 to the D50 of the secondary particles is 0.032.

[0153] The elemental composition at different locations in the P6 profile was determined by energy dispersive X-ray spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in P6, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 14.2%.

[0154] Example 7

[0155] The method of Example 4 is different in that, in step (3), during the two-stage lithium supplementation sintering process, the temperature is first raised to 700°C at a heating rate of 8°C / min and sintered at a constant temperature for 3 hours, and then raised to 755°C at a heating rate of 0.5°C / min and sintered at a constant temperature for 2 hours. Other steps and conditions are the same as in Example 4, and a gradient cathode material (denoted as P7) is prepared.

[0156] P7 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of P7 satisfies the chemical formula LiNi. 0.90 Co 0.06 Mn 0.02 Al 0.02 Zr 0.002 Ce 0.001 O2;

[0157] P7 has a D90 of 20.7 μm, a D50 of 13.4 μm, a D10 of 9.2 μm, and a (D90-D10) / D50 ratio of 0.86.

[0158] The minor axis diameter of the primary particles of P7 is 230 nm; the ratio of the minor axis diameter of the primary particles of P7 to the D50 of the secondary particles is 0.017.

[0159] The elemental composition at different locations on the P7 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in P7, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 15.9%.

[0160] Example 8

[0161] The method of Example 4 differs in that, in step (1), when the precursor obtained from the coprecipitation reaction grows to a D50 of 1.5 μm (i.e., r1 = 1.5 μm, r1 / R = 10:100), zirconium sulfate (first compound) is added; when the precursor obtained from the coprecipitation reaction grows to a D50 of 13.1 μm (i.e., r2 = 13.1 μm, r2 / R = 90:100), cerium nitrate (second compound) is added; wherein, the amounts of the first compound and the second compound fed satisfy the following relationship: (r1 3 / R 3) / (n1 / n1+n2)=0.002 (where n1 is the amount of the first compound fed as dopant element Zr, and n2 is the amount of the second compound fed as dopant element Ce). Other steps and conditions are the same as in Example 4, and a gradient cathode material (denoted as P8) is prepared.

[0162] P8 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of P8 satisfies the chemical formula LiNi. 0.90 Co 0.06 Mn 0.02 Al 0.02 Zr 0.002 Ce 0.001 O2;

[0163] P8 has a D90 of 20.7 μm, a D50 of 13.5 μm, a D10 of 9.2 μm, and a (D90-D10) / D50 ratio of 0.85.

[0164] The minor axis diameter of the primary particles of P8 is 220 nm; the ratio of the minor axis diameter of the primary particles of P8 to the D50 of the secondary particles is 0.016.

[0165] The elemental composition at different locations on the P8 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in P8, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 10.2%.

[0166] Comparative Example 1

[0167] The method of Example 1 is different in that, in step (1), nickel sulfate, cobalt sulfate, manganese sulfate and water are respectively prepared into mixed solution A (in mixed solution A, the molar ratio of Ni:(Co+Mn) is 49:1) and mixed solution B (in mixed solution B, the molar ratio of Ni:(Co+Mn) is 0.5:1); under N2 atmosphere, the above mixed solution A is first placed in the reactor, and then the above mixed solution B is continuously added to the reactor, while ammonia water and NaOH solution are added to the reactor respectively to carry out co-precipitation reaction;

[0168] When the precursor obtained from the coprecipitation reaction grows to a D50 of 5.5 μm (i.e., r1 = 5.5 μm, r1 / R = 42:100), magnesium chloride (the first compound) is added; when the precursor obtained from the coprecipitation reaction grows to a D50 of 9.2 μm (i.e., r2 = 9.2 μm, r2 / R = 71:100), magnesium chloride (the second compound) is added; wherein the amounts of the first and second compounds fed satisfy the following relationship: (r1 3 / R 3 ) / (n1 / n1+n2)=0.12 (where n1 is the amount of the first compound fed in terms of the doping element Mg, and n2 is the amount of the second compound fed in terms of the doping element Mg);

[0169] The coprecipitation reaction was carried out at a temperature of 67℃, a stirring rate of 650 rpm, and a pH of 11.4. After the reaction, the resulting product system was subjected to solid-liquid separation, washing, drying, and sieving to obtain the doped gradient precursor (denoted as DM1).

[0170] The chemical composition of DM1 satisfies the chemical formula (Ni 0.90 Co 0.05 Mn 0.05 Mg 0.001 (OH)2, the D50 (i.e., R) of DM1 is 13 μm;

[0171] The elemental composition at different locations along the DM1 profile was determined by X-ray energy dispersive spectroscopy (EDS). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in DM1, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 64.3%.

[0172] All other steps and conditions are the same as in Example 1, and a gradient cathode material (denoted as D1) is prepared.

[0173] D1 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of D1 satisfies the chemical formula LiNi. 0.90 Co 0.05 Mn 0.05 Mg 0.001 O2;

[0174] A scanning electrical test was performed on D1, and the results are as follows: Figure 2 As shown, Figure 2 The primary grain coarsening of the gradient material is visible, resulting in poor uniformity.

[0175] The D90 of D1 is 14.7 μm, the D50 is 11.8 μm, the D10 is 9.8 μm, and the (D90-D10) / D50 is 0.42.

[0176] The minor axis diameter of the primary particle of D1 is 560 nm; the ratio of the minor axis diameter of the primary particle of D1 to the D50 of the secondary particle is 0.047.

[0177] The elemental composition at different locations in the D1 profile was determined by X-ray energy dispersive spectroscopy (EDS) (results are shown in Table 1). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm. 2 -0.55um 2 It was found that in D1, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 6.2%.

[0178] Comparative Example 2

[0179] The doped gradient precursor was prepared according to the method and parameters of step (1) in Example 1. The difference is that steps (2) and (3) were combined into a one-stage sintering process. That is, lithium hydroxide (D50 is 11.0 μm) and the doped gradient precursor were mixed evenly in a high-speed mixer at a weight ratio of 0.466:1. The resulting mixture was loaded into a sagger and transferred to a kiln with a mixed atmosphere of air and oxygen (oxygen volume concentration is 95%) for one-stage sintering. The pressure difference between the internal and external air pressure of the kiln was 3±1 Pa. The temperature was raised to 760°C at a heating rate of 3°C / min and sintered at a constant temperature for 10 h. The sintered product was naturally cooled to room temperature and then pulverized to obtain the gradient cathode material (denoted as D2).

[0180] D2 is a lithium-containing metal oxide compound with a layered structure. The chemical composition of D2 satisfies the chemical formula LiNi. 0.90 Co 0.05 Mn 0.05 W 0.001 O2;

[0181] D2 has a D90 of 10.2 μm, a D50 of 13.0 μm, a D10 of 15.0 μm, and a (D90-D10) / D50 ratio of 0.37.

[0182] The minor axis diameter of the primary particle of D2 is 420 nm; the ratio of the minor axis diameter of the primary particle of D2 to the D50 of the secondary particle is 0.032.

[0183] The elemental composition at different locations in the D2 profile was determined by X-ray energy dispersive spectroscopy (EDS) (results are shown in Table 1). The selected test locations were the core, halfway between the core and the surface (half the radius), and the surface, with a selected area of ​​0.5 μm.2 -0.55um 2 It was found that in D2, the Ni concentration was distributed in a gradient from the core to the surface and gradually decreased, and the Ni concentration difference between the core and the surface was 30.2%.

[0184] Table 1

[0185]

[0186]

[0187] Test case

[0188] CR2032 button cells were fabricated using the aforementioned cathode materials P1-P8 and D1-D2. The fabrication process is as follows:

[0189] The positive electrode materials (P1-P8, D1-D2), conductive agent carbon black SP, and solvent NMP were mixed at a weight ratio of 1:0.02:0.54 to obtain a positive electrode slurry. This slurry was then uniformly coated onto clean aluminum foil, dried, and used to prepare a positive electrode sheet. (Differential scanning calorimetry (DSC) was performed on the positive electrode sheet to test the thermal stability of the positive electrode material; the results are shown in Table 2.) Using a CR2032 battery casing, the above electrodes were used as the positive electrode, lithium metal sheets as the negative electrode, an 18mm 2325 separator, and Jinniu JN908-6 electrolyte. The cells were assembled sequentially to obtain button cells (denoted as B1-B8 and DB1-DB2, respectively). The assembled cells were allowed to stand for 24 hours, after which their electrical performance was tested.

[0190] The prepared batteries B1-B8 and DB1-DB2 were subjected to rate performance testing and cycle performance testing.

[0191] Rate performance test conditions: set the charge and discharge voltage to 3.0-4.3V, the charge rate to 0.2C, and the discharge rate to 5C.

[0192] Cyclic performance test conditions: charge rate 1C, discharge rate 1C, voltage range 3.0-4.3V, temperature 25±1℃, and number of cycles 50. The results are shown in Table 2.

[0193] Table 2

[0194] B1 225 189.1 95.6 B2 219 186.4 93.8 B3 215 188.3 91.3 B4 213 184.8 90.2 B5 210 184.1 88.1 B6 208 182.3 87.4 B7 207 181.5 86.9 B8 204 183.3 85.6 DB1 200 178.6 80.1 DB2 201 177.2 80.4

[0195] As can be seen from the above embodiments, comparative examples, and data in Tables 1 and 2, the method for preparing gradient cathode materials according to the present invention is beneficial for maintaining the transition metal concentration gradient, suppressing particle coarsening, and the two-stage sintering of pre-sintering and lithium supplementation can improve the structural stability of cathode material particles. The resulting gradient material particles have increased strength and better thermal stability, rate performance, and cycle performance.

[0196] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a gradient cathode material, characterized in that, include: (1) Co-precipitate the metal salt to obtain the doped gradient precursor; (2) The doped gradient precursor and the first lithium source are pre-sintered together to obtain lithium-poor oxide; The lithium-poor oxide was subjected to XRD testing, and the I of the lithium-poor oxide was... 003 / I 104 The peak intensity ratio is 0.5-1.5; (3) The lithium-poor oxide and the second lithium source are subjected to a two-stage lithium-supplemented sintering process to obtain a gradient cathode material; In the co-precipitation process, the dopant element is added in two stages; when the precursor obtained by the co-precipitation grows to D50 of r1, a first compound containing dopant element M is added; wherein, r1 / R = (30-50):

100. When the precursor obtained by co-precipitation grows to D50 of r2, a second compound containing doped element M is added; wherein, r2 / R = (60-80):100; Wherein, R is the D50 value of the doped gradient precursor; the D50 of the doped gradient precursor is 3-20 μm; The chemical composition of the doped gradient precursor satisfies the chemical formula (Ni x D y M z ) (OH)2, where, Element D is selected from at least one of Mn, Co, Al, Zr, Ti, and Mg; The oxide of doped element M satisfies the chemical formula M a O b Where a and b are positive integers, and b / a > 1.5; 0.8≤x<1, x+y=1, 0.0002≤z≤0.02; the dopant element M is selected from at least one of W, Mo, Nb and Sb; In the doped gradient precursor, the Ni concentration is distributed in a gradient from the core to the surface of the doped gradient precursor and gradually decreases, and the Ni concentration difference between the core and the surface is not less than 15 mol.

2. The method according to claim 1, wherein, The feed amounts of the first compound and the second compound satisfy the following relationship: (r1) 3 / R 3 ) / (n1 / n1+n2)≤1; Wherein, n1 is the amount of the first compound fed in terms of dopant element M, and n2 is the amount of the second compound fed in terms of dopant element M. The amounts of n1 and n2 are expressed in terms of moles.

3. The method according to claim 1 or 2, wherein, In step (2), the weight ratio of the first lithium source to the doped gradient precursor is (0.355-0.456):1; And / or, the pre-sintering conditions include: a heating rate of 3-6℃ / min, a sintering temperature of 300-650℃, and a sintering time of 3-10h.

4. The method according to claim 1 or 2, wherein, In step (3), the weight ratio of the second lithium source to lithium-poor oxide is (0.001-0.131):

1.

5. The method according to claim 1 or 2, wherein, The weight ratio of the first lithium source to the doped gradient precursor and the weight ratio of the second lithium source to the lithium-poor oxide satisfy the following relationship: 0.444 < Q1 + Q2 ≤ 0.493; where Q1 is the weight ratio of the first lithium source to the doped gradient precursor and Q2 is the weight ratio of the second lithium source to the lithium-poor oxide.

6. The method according to claim 1 or 2, wherein, In step (3), the lithium replenishment two-stage sintering is divided into a first stage sintering and a second stage sintering performed sequentially.

7. The method according to claim 6, wherein, The conditions for the first sintering stage include: a heating rate of 5-8℃ / min, a sintering temperature of 350-750℃, and a sintering time of 3-10h.

8. The method according to claim 6, wherein, The sintering temperature of the first sintering stage is 50-100°C higher than the sintering temperature of the pre-sintering stage.

9. The method according to claim 6, wherein, The conditions for the second stage of sintering include: a heating rate of 0.05-0.5℃ / min, a sintering temperature of 600-900℃, and a sintering time of 2-5h.

10. A gradient cathode material prepared by the method of any one of claims 1-9.

11. The gradient cathode material according to claim 10, wherein, The gradient cathode material The chemical composition of LiNi satisfies the chemical formula x D y M z O, wherein element D is selected from at least one of Mn, Co, Al, Zr, Ti and Mg; The oxide of doped element M satisfies the chemical formula M a O b Where a and b are positive integers, and b / a > 1.5; the dopant element M is selected from at least one of W, Mo, Nb and Sb; 0.8≤x<1, x+y=1, 0.0002≤z≤0.02; In the gradient cathode material, the Ni concentration is distributed in a gradient from the core to the surface and gradually decreases, and the Ni concentration difference between the core and the surface is not less than 10 mol.

12. The gradient cathode material according to claim 10 or 11, wherein, The D50 of the gradient cathode material is 3-20 μm; And / or, the D90, D50, and D10 of the gradient cathode material satisfy: 0.3 ≤ (D90 - D10) / D50 ≤ 1.5; And / or, the minor axis diameter of the primary particles of the gradient cathode material is 150-500 nm; And / or, the ratio of the minor axis diameter of the primary particles to the D50 of the secondary particles of the gradient cathode material is 0.0075-0.

17.

13. A lithium-ion battery comprising the gradient cathode material according to any one of claims 10-12.

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