Boron gradient doped positive electrode precursor, preparation method thereof, positive electrode material and battery

Abstract

The invention provides a boron gradient-doped positive electrode precursor and a preparation method thereof, a positive electrode material and a battery. The positive electrode precursor comprises a boron-doped ternary material core and a boron-doped ternary material layer coated outside the boron-doped ternary material core, the mass fraction of the boron element in the boron-doped ternary material core is lower than that of the boron element in the boron-doped ternary material layer. In the boron gradient-doped positive electrode precursor provided by the invention, boron doping is performed in the boron-doped ternary material core and the boron-doped ternary material layer, so that a B-O bond with relatively high bond energy is formed, and lattice stress accumulation in the positive electrode precursor is reduced, thereby improving the structural stability and thermal stability of the positive electrode precursor and the positive electrode material; in addition, through gradient doping of boron, the electrochemical performance of the positive electrode material is ensured, the surface and interface structure of the positive electrode precursor is strengthened, the expansion of cracks is inhibited, and the structural stability of the positive electrode precursor is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a boron gradient-doped positive electrode precursor, and in particular to a boron gradient-doped positive electrode precursor and a preparation method thereof, a positive electrode material and a battery. Background Art

[0002] With the rapid development of new energy vehicles and the energy storage industry, the research and development of high-energy-density lithium-ion battery cathode materials has become a focus of industry attention. Nickel-cobalt-manganese ternary cathode materials (NCM) are considered an ideal choice for next-generation power batteries due to their high specific capacity (≥180mAh / g) and energy density (≥700Wh / kg). However, these materials still face numerous challenges in practical application.

[0003] First, the nickel-cobalt-manganese ternary cathode materials disclosed in the prior art have the problem of insufficient structural stability: the ternary materials with high nickel content (Ni≥60%) have serious structural degradation during the charge and discharge process, which is mainly manifested in the mixed arrangement of cations (Ni 2+ Occupy Li + The crystal structure distortion caused by the irreversible phase transition (H2→H3 phase transition) during the cycle process and the lattice stress caused by the irreversible phase transition (H2→H3 phase transition) cause micro cracks inside the material particles, which accelerates the capacity decay.

[0004] Secondly, the nickel-cobalt-manganese ternary cathode material disclosed in the prior art also has thermal safety risks: in the highly charged state (delithiation state), the crystal structure of the nickel-cobalt-manganese ternary cathode material is unstable, and the oxygen atoms in the material lattice and the transition metal (especially Ni with high nickel content) are unstable. 3+ / Ni 4+ ) significantly reduced the bonding strength, and the lattice oxygen (O 2- ) is easily released in the form of O2. The released oxygen undergoes a violent oxidation reaction with the organic solvent in the electrolyte, releasing a large amount of heat, which leads to thermal safety hazards.

[0005] Based on the defects of nickel-cobalt-manganese ternary cathode materials, various methods are used in the prior art to modify nickel-cobalt-manganese ternary cathode materials. The modification methods used in the prior art mainly include: first, bulk doping, that is, uniform doping with elements such as Al, Mg and Ti, which can partially suppress cation mixing, but the modification effect is limited. Second, uniform doping with boron, B 3+ The ionic radius is small and it is easy to enter the crystal lattice, forming a strong BO bond and stabilizing the crystal structure. However, the uniform doping method with boron elements still cannot effectively improve the structural stability and thermal stability of the ternary positive electrode material.

[0006] CN117766706A discloses a boron-doped diamond-coated high-power, long-cycle ternary cathode material and its preparation method. The preparation method comprises the following steps: S1, crushing the ternary cathode material and dispersing it in a diamond suspension, seeding it under ultrasonic conditions, filtering it, and drying it to obtain a ternary cathode material seeded with diamond crystals; S2, placing the ternary cathode material seeded with diamond crystals in a chemical vapor deposition device, and depositing it by introducing gaseous carbon and boron sources to obtain a boron-doped diamond-coated ternary cathode material. However, the structural stability and thermal stability of this ternary cathode material still cannot meet the requirements of practical applications.

[0007] CN117800407A discloses a Co-gradient doped and coated ternary cathode material, its preparation method, and application. The method for preparing the Co-gradient doped and coated ternary cathode material provided in this disclosure comprises the following steps: 1) mixing a nickel-cobalt precursor, a lithium source, a cobalt source, an aluminum source, and a doping metal compound to obtain a mixture; and 2) sintering the mixture from step 1) to obtain the Co-gradient doped and coated ternary cathode material. However, modifying the ternary cathode material through Co-gradient doping and coating is also difficult to effectively improve the structural and thermal stability of the ternary cathode material.

[0008] In summary, the ternary cathode materials disclosed in the prior art suffer from insufficient structural and thermal stability, and the existing methods for modifying ternary cathode materials still fail to effectively improve their structural and thermal stability. Therefore, the development and design of a novel boron-gradient-doped cathode precursor, its preparation method, cathode material, and battery are crucial. Summary of the Invention

[0009] In view of the deficiencies in the prior art, the object of the present invention is to provide a boron-gradient-doped positive electrode precursor and a preparation method thereof, a positive electrode material and a battery. In the boron-gradient-doped positive electrode precursor provided by the present invention, boron is doped in both the core of the boron-doped ternary material and the boron-doped ternary material layer, thereby forming BO bonds with higher bond energy and reducing the lattice stress accumulation in the positive electrode precursor, thereby improving the structural stability and thermal stability of the positive electrode precursor and the positive electrode material prepared using the positive electrode precursor; in addition, through the gradient doping of boron, while ensuring the electrochemical properties of the positive electrode material, the surface and interfacial structure of the positive electrode precursor is strengthened, the crack expansion from the surface to the interior of the positive electrode precursor is suppressed, and the structural stability of the positive electrode precursor is improved.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a boron gradient-doped cathode precursor, the cathode precursor comprising a boron-doped ternary material core and a boron-doped ternary material layer coated on the outside of the boron-doped ternary material core;

[0012] The mass fraction of the boron element in the boron-doped ternary material core is lower than the mass fraction of the boron element in the boron-doped ternary material layer.

[0013] In the positive electrode precursor provided by the present invention, boron is doped in both the boron-doped ternary material core and the boron-doped ternary material layer. Since the boron element has a small ionic radius, it is embedded in the crystal lattice to form a BO bond with a higher bond energy, which effectively enhances the rigidity of the crystal structure and inhibits oxygen loss and phase change at high temperatures, thereby enhancing the structural stability and thermal stability of the positive electrode precursor and the positive electrode material prepared using the positive electrode precursor; in addition, boron doping also reduces the accumulation of lattice stress in the positive electrode precursor, further improving the structural stability of the positive electrode precursor and the positive electrode material prepared using the positive electrode precursor.

[0014] In the positive electrode precursor provided by the present invention, the mass fraction of the boron element in the boron-doped ternary material core is lower than the mass fraction of the boron element in the boron-doped ternary material layer. The boron-doped ternary material core has a lower boron concentration. While maintaining the lattice integrity of the boron-doped ternary material core, it avoids the obstruction of lithium diffusion caused by excessive doping, thereby ensuring that the positive electrode material prepared with the positive electrode precursor has good electrochemical properties; the boron-doped ternary material layer has a higher boron concentration, which improves the structural stability and thermal stability of the boron-doped ternary material layer, strengthens the surface and interface structure of the positive electrode precursor, and inhibits the expansion of cracks from the surface to the inside of the positive electrode precursor, thereby improving the structural stability of the positive electrode precursor.

[0015] To sum up, in the boron-gradient-doped positive electrode precursor provided by the present invention, boron is doped in both the core of the boron-doped ternary material and the boron-doped ternary material layer, forming BO bonds with higher bond energy and reducing the lattice stress accumulation in the positive electrode precursor, thereby improving the structural stability and thermal stability of the positive electrode precursor and the positive electrode material prepared using the positive electrode precursor; in addition, through the gradient doping of boron, while ensuring the electrochemical properties of the positive electrode material, the surface and interfacial structure of the positive electrode precursor is strengthened, the cracks are inhibited from expanding from the surface to the interior of the positive electrode precursor, and the structural stability of the positive electrode precursor is improved.

[0016] Preferably, taking the mass fraction of the boron-doped ternary material core as percent, the mass fraction of the boron element in the boron-doped ternary material core is 0.1 to 1.5 wt%, for example, it can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt% or 1.5 wt%, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0017] In the present invention, when the mass fraction of the boron element in the core of the boron-doped ternary material is 0.1-1.5wt%, the positive electrode precursor and the positive electrode material have better performance. This is because when the mass fraction of the boron element in the core of the boron-doped ternary material is 0.1-1.5wt%, a strong BO bond is formed by embedding an appropriate amount of boron element into the crystal lattice, thereby enhancing the rigidity of the core crystal structure, inhibiting cation mixing and high-temperature oxygen loss, and avoiding the obstruction of lithium ion diffusion caused by excessive doping, thereby maintaining the integrity of the lattice; the low boron concentration in the core and the high boron in the outer layer are connected through a gradient transition zone, so that the boron content changes linearly, reducing the stress concentration caused by lattice mutation, and synergistically inhibiting the propagation of bulk cracks.

[0018] Preferably, the D50 particle size of the boron-doped ternary material core is 2 to 5 μm, for example, it can be 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.5 μm, 4.8 μm or 5.0 μm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0019] Preferably, taking the mass fraction of the boron-doped ternary material layer as percent, the mass fraction of the boron element in the boron-doped ternary material layer is 1.5 to 3 wt%, for example, it can be 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt% or 3.0 wt%, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0020] In the present invention, when the mass fraction of boron element in the boron-doped ternary material layer is 1.5-3wt%, the positive electrode precursor and the positive electrode material have better performance. This is because this boron content range can not only enhance the synergistic effect between the boron-doped ternary material layer and the lithium fluoride coating layer, forming a stable BOF bonded transition layer to inhibit electrolyte corrosion and transition metal dissolution, but also avoid the blockage of lithium ion transmission channels caused by excessive boron enrichment, thereby balancing the structural stability and electrochemical kinetic performance of the material.

[0021] Preferably, the thickness of the boron-doped ternary material layer is 4 to 7 μm, for example, it can be 4.0 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5.0 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6.0 μm, 6.2 μm, 6.5 μm, 6.8 μm or 7.0 μm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0022] Preferably, a gradient transition zone is further included between the boron-doped ternary material core and the boron-doped ternary material layer;

[0023] In the gradient transition region, the boron content increases linearly from the direction close to the boron-doped ternary material core to the direction close to the boron-doped ternary material layer.

[0024] In the present invention, a gradient transition zone exists between the boron-doped ternary material core and the boron-doped ternary material layer. The gradient transition zone can not only serve as a buffer layer between the boron-doped ternary material core and the boron-doped ternary material layer, thereby absorbing the stress between the boron-doped ternary material core and the boron-doped ternary material layer; it can also make the boron content between the boron-doped ternary material core, the gradient transition zone and the boron-doped ternary material layer change gradually, reduce lattice mutation, and inhibit crack propagation, thereby improving the structural stability of the positive electrode precursor and the positive electrode material prepared with the positive electrode precursor.

[0025] Preferably, the thickness of the gradient transition zone is 200 to 500 nm, for example, it can be 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm or 500 nm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0026] Preferably, the positive electrode precursor further includes a lithium fluoride coating layer coated on the outside of the boron-doped ternary material layer.

[0027] The nickel-cobalt-manganese ternary positive electrode material disclosed in the prior art also has the problem of insufficient interface stability: the surface of the nickel-cobalt-manganese ternary positive electrode material is prone to side reactions with the electrolyte to form an unstable CEI film. In addition, the transition metal ions in the nickel-cobalt-manganese ternary positive electrode material are easily dissolved in the electrolyte, resulting in battery performance degradation.

[0028] In the present invention, the lithium fluoride coating layer can physically isolate the positive electrode material prepared by the positive electrode precursor from direct contact with the electrolyte, inhibit the corrosion of the electrolyte decomposition products, and reduce surface side reactions and transition metal dissolution, thereby improving the interface structure stability of the positive electrode material prepared by the positive electrode precursor, thereby improving the electrochemical performance of the battery containing the positive electrode material.

[0029] Preferably, the thickness of the lithium fluoride coating layer is 50 to 300 nm, for example, it can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm or 300 nm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0030] Preferably, a BOF bonding transition layer is further provided between the boron-doped ternary material layer and the lithium fluoride coating layer.

[0031] In the present invention, the lithium fluoride in the lithium fluoride coating layer reacts with the boron in the boron-doped ternary material layer to generate a BOF bonded transition layer with a thermal decomposition temperature higher than 400°C. The BOF bonded transition layer has both high ionic conductivity and strong chemical bonding, which not only alleviates the lattice stress caused by volume change during charging and discharging, but also inhibits oxygen release and phase change heat release at high temperature through the strong covalency of the BOF bond, thereby synergistically enhancing the structural stability and thermal stability of the positive electrode precursor.

[0032] Preferably, the thickness of the BOF bonding transition layer is 200 to 800 nm, for example, it can be 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm or 800 nm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0033] In the present invention, when the thickness of the BOF bonding transition layer is 200 to 800 nm, the positive electrode precursor and the positive electrode material have better performance. This is because this thickness range can form a continuous and dense BOF bonding interface layer, which can effectively inhibit oxygen release and phase change heat release at high temperature through strong covalent bonding, and maintain a fast lithium ion transmission channel, thereby synergistically improving the electrochemical performance and thermal stability of the positive electrode material prepared using the positive electrode precursor.

[0034] Preferably, based on the total mass of the positive electrode precursor, the mass fraction of the boron element in the positive electrode precursor is 0.1 to 3 wt%, for example, it can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2.0 wt%, 2.5 wt% or 3.0 wt%, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the chemical formula of the positive electrode precursor is Ni x Co y Mn z B w (OH)2;

[0036] Among them, 0.88≤x≤0.97, 0.01≤y≤0.05, 0.005≤z≤0.04, 0.015≤w≤0.03, x+y+z+w=1.

[0037] In the present invention, 0.88≤x≤0.97, and the value of x can be, for example, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96 or 0.97, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In the present invention, 0.01≤y≤0.05, and the value of y can be, for example, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045 or 0.05, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0039] In the present invention, 0.005≤z≤0.04, and the value of z can be, for example, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035 or 0.04, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0040] In the present invention, 0.015≤w≤0.03, and the value of w can be, for example, 0.015, 0.018, 0.02, 0.022, 0.025, 0.028 or 0.03, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0041] In a second aspect, the present invention provides a method for preparing the positive electrode precursor according to the first aspect, the preparation method comprising:

[0042] (1) adding a metal mixed salt solution, a precipitant solution, a complexing agent solution and a boron source to a reaction base liquid in parallel to form a reaction solution, and performing a first coprecipitation reaction in the reaction solution to obtain a solution containing a boron-doped ternary material core;

[0043] (2) adding the metal mixed salt solution, the precipitant solution, the complexing agent solution and the boron source in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution, and performing a second coprecipitation reaction in the reaction solution to obtain a positive electrode precursor;

[0044] The concentration of the boron source in the reaction solution of step (1) is less than the concentration of the boron source in the reaction solution of step (2).

[0045] Preferably, the method for preparing the metal mixed salt solution in step (1) and step (2) comprises: adding nickel salt, cobalt salt and manganese salt to a solvent to obtain the metal mixed salt solution in step (1) and step (2).

[0046] Preferably, the precipitant in the precipitant solution in step (1) and step (2) independently comprises any one of sodium hydroxide, potassium hydroxide, sodium carbonate or ammonium carbonate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of sodium hydroxide and potassium hydroxide, a combination of sodium carbonate and ammonium carbonate, a combination of sodium hydroxide, sodium carbonate and ammonium carbonate, or a combination of potassium hydroxide, sodium carbonate and ammonium carbonate.

[0047] Preferably, the mass concentration of the precipitant in the precipitant solution in step (1) and step (2) is 20 to 40 wt%, for example, it can be 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt% or 40 wt%, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0048] Preferably, the complexing agent in the complexing agent solution of step (1) and step (2) independently includes any one of ammonia, ethylenediaminetetraacetic acid, citric acid or oxalic acid, or a combination of at least two of them. Typical but non-limiting combinations include a combination of ammonia and ethylenediaminetetraacetic acid, a combination of citric acid and oxalic acid, a combination of ammonia, citric acid and oxalic acid, or a combination of ethylenediaminetetraacetic acid, citric acid and oxalic acid.

[0049] Preferably, the mass concentration of the complexing agent in the complexing agent solution in step (1) and step (2) is 10 to 30 wt%, for example, it can be 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt% or 30 wt%, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0050] Preferably, in the first coprecipitation reaction in step (1), the pH value of the reaction solution is controlled to be 9.0-10.0, for example, it can be 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9 or 10.0, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable, preferably 9.6-9.8.

[0051] Preferably, in the first coprecipitation reaction of step (1), the ammonia concentration in the reaction solution is controlled to be 2-3 g / L, for example, it can be 2.0 g / L, 2.1 g / L, 2.2 g / L, 2.3 g / L, 2.4 g / L, 2.5 g / L, 2.6 g / L, 2.7 g / L, 2.8 g / L, 2.9 g / L or 3.0 g / L, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable, preferably 2.5 to 3 g / L.

[0052] Preferably, in the first coprecipitation reaction in step (1), the concentration of boron in the reaction solution is controlled to be 1200-1800 ppm, for example, it can be 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm or 1800 ppm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0053] Preferably, the boron source added to the first co-precipitation reaction in step (1) includes boric acid and borate.

[0054] Preferably, the boron source in step (1) comprises a boric acid solution. During the parallel addition in step (1), the concentration of boric acid in the added boric acid solution is 3.0 to 6.0 g / L; and the addition flow rate of the boric acid solution is 1.0 to 2.0 L / h.

[0055] In the present invention, during the parallel addition in step (1), the concentration of boric acid in the added boric acid solution is 3.0 to 6.0 g / L, for example, 3.0 g / L, 3.2 g / L, 3.5 g / L, 3.8 g / L, 4.0 g / L, 4.2 g / L, 4.5 g / L, 4.8 g / L, 5.0 g / L, 5.2 g / L, 5.5 g / L, 5.8 g / L or 6.0 g / L, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 3.6 to 5.4 g / L.

[0056] In the present invention, during the parallel addition in step (1), the addition flow rate of the boric acid solution is 1.0 to 2.0 L / h, for example, it can be 1.0 L / h, 1.1 L / h, 1.2 L / h, 1.3 L / h, 1.4 L / h, 1.5 L / h, 1.6 L / h, 1.7 L / h, 1.8 L / h, 1.9 L / h or 2.0 L / h, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable, preferably 1.2 to 1.8 L / h.

[0057] Preferably, the borate comprises sodium borate.

[0058] Preferably, the first coprecipitation reaction in step (1) is also accompanied by stirring at a speed of 550 to 650 rpm, for example, it can be 550 rpm, 560 rpm, 570 rpm, 580 rpm, 590 rpm, 600 rpm, 610 rpm, 620 rpm, 630 rpm, 640 rpm or 650 rpm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0059] Preferably, in the first coprecipitation reaction in step (1), the temperature of the reaction solution is controlled to be 55-65°C, for example, it can be 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C or 65°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0060] Preferably, the time ratio of the first coprecipitation reaction in step (1) to the second coprecipitation reaction in step (2) is 1:(1-2), for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0061] Preferably, in the second coprecipitation reaction in step (2), the pH value of the reaction solution is controlled to be 11.0-12.0, for example, it can be 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9 or 12.0, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable, preferably 11.2-11.4.

[0062] Preferably, in the second coprecipitation reaction of step (2), the ammonia concentration in the reaction solution is controlled to be 5 to 7 g / L, for example, it can be 5.0 g / L, 5.2 g / L, 5.4 g / L, 5.6 g / L, 5.8 g / L, 6.0 g / L, 6.2 g / L, 6.4 g / L, 6.6 g / L, 6.8 g / L or 7.0 g / L, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable, preferably 5.5 to 6.5 g / L.

[0063] Preferably, in the second coprecipitation reaction in step (2), the concentration of boron in the reaction solution is controlled to be 2700-3300 ppm, for example, it can be 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3100 ppm, 3200 ppm or 3300 ppm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0064] Preferably, the boron source added to the second co-precipitation reaction in step (2) includes boric acid and borate.

[0065] Preferably, the boron source in step (2) comprises a boric acid solution. During the parallel addition in step (2), the concentration of boric acid in the added boric acid solution is 8.0 to 11.0 g / L; and the addition flow rate of the boric acid solution is 2.0 to 4.0 L / h.

[0066] In the present invention, during the parallel addition in step (2), the concentration of boric acid in the added boric acid solution is 8.0 to 11.0 g / L, for example, it can be 8.0 g / L, 8.2 g / L, 8.5 g / L, 8.8 g / L, 9.0 g / L, 9.2 g / L, 9.5 g / L, 9.8 g / L, 10.0 g / L, 10.2 g / L, 10.5 g / L, 10.8 g / L or 11.0 g / L, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable, preferably 8.2 to 10.8 g / L.

[0067] In the present invention, during the parallel addition in step (2), the addition flow rate of the boric acid solution is 2.0 to 4.0 L / h, for example, it can be 2.0 L / h, 2.2 L / h, 2.4 L / h, 2.6 L / h, 2.8 L / h, 3.0 L / h, 3.2 L / h, 3.4 L / h, 3.6 L / h, 3.8 L / h or 4.0 L / h, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable, preferably 1.8 to 3.6 L / h.

[0068] Preferably, the borate comprises sodium borate.

[0069] Preferably, the second coprecipitation reaction in step (2) is also accompanied by stirring at a speed of 550 to 650 rpm, for example, it can be 550 rpm, 560 rpm, 570 rpm, 580 rpm, 590 rpm, 600 rpm, 610 rpm, 620 rpm, 630 rpm, 640 rpm or 650 rpm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0070] Preferably, in the second coprecipitation reaction in step (2), the temperature of the reaction solution is controlled to be 55-65°C, for example, it can be 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C or 65°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0071] Preferably, the preparation method further comprises step (2) after the second coprecipitation reaction:

[0072] The precipitate obtained by the second coprecipitation reaction, lithium fluoride and a solvent are mixed to obtain a mixed slurry, and the obtained mixed slurry is heat-treated to obtain a positive electrode precursor.

[0073] Preferably, the mass ratio of the precipitate obtained by the second coprecipitation reaction in the mixing to lithium fluoride is 1:(0.01-0.02), for example, it can be 1:0.01, 1:0.011, 1:0.012, 1:0.013, 1:0.014, 1:0.015, 1:0.016, 1:0.017, 1:0.018, 1:0.019 or 1:0.02, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0074] Preferably, the solid content of the mixed slurry is 20-30%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%, but it is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0075] Preferably, the mixing method includes heating and stirring, and the heating and stirring temperature is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0076] Preferably, the heat treatment includes a first heating, a first heat preservation, a second heating and a second heat preservation performed in sequence.

[0077] Preferably, the heating rate of the first heating is 5-8°C / min, and the end temperature is 400-500°C.

[0078] In the present invention, the heating rate of the first heating is 5 to 8°C / min, for example, it can be 5°C / min, 5.2°C / min, 5.5°C / min, 5.8°C / min, 6°C / min, 6.2°C / min, 6.5°C / min, 6.8°C / min, 7°C / min, 7.2°C / min, 7.5°C / min, 7.8°C / min or 8°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0079] In the present invention, the endpoint temperature of the first heating is 400-500°C, for example, it can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C or 500°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0080] Preferably, the first insulation time is 1 to 2 hours, for example, it can be 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0081] Preferably, the heating rate of the second heating is 4-6°C / min, and the end temperature is 500-600°C.

[0082] In the present invention, the heating rate of the second heating is 4 to 6°C / min, for example, it can be 4°C / min, 4.2°C / min, 4.5°C / min, 4.8°C / min, 5°C / min, 5.2°C / min, 5.5°C / min, 5.8°C / min or 6°C / min, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0083] In the present invention, the endpoint temperature of the second heating is 400-500°C, for example, it can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C or 500°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0084] Preferably, the first insulation time is 2 to 3 hours, for example, it can be 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0085] Preferably, the preparation method further comprises step (2) washing and drying performed sequentially between the second coprecipitation reaction and the mixing.

[0086] Preferably, the washing comprises alkali washing and water washing performed sequentially.

[0087] Preferably, the washing liquid used in the alkaline washing process includes a NaOH solution with a mass fraction of 3-4wt%, for example, it can be 3.0wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt%, 3.6wt%, 3.7wt%, 3.8wt%, 3.9wt% or 4.0wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0088] Preferably, the drying temperature is 80-160°C, for example, it can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or 160°C, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable, preferably 120-160°C.

[0089] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises:

[0090] (1) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution, adding the metal mixed salt solution, precipitant solution, complexing agent solution and boric acid solution to a reaction base liquid in parallel to form a reaction solution, controlling the pH value of the reaction solution to 9.0-10.0, the ammonia concentration to 2-3 g / L, the boron concentration to 1200-1800 ppm and the temperature to 55-65° C., and stirring at a speed of 550-650 rpm to perform a first coprecipitation reaction in the reaction solution to obtain a solution containing a boron-doped ternary material core;

[0091] (2) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution, adding the metal mixed salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution, controlling the pH value of the reaction solution to 11.0-12.0, the ammonia concentration to 5-7 g / L, the boron concentration to 2700-3300 ppm and the temperature to 55-65° C., stirring at a speed of 550-650 rpm, carrying out a second coprecipitation reaction in the reaction solution, filtering, and sequentially washing the obtained solid with alkali and water, and then drying at 80-160° C. to obtain a precipitate;

[0092] The ratio of the time of the first coprecipitation reaction in step (1) to the time of the second coprecipitation reaction in step (2) is 1:(1-2);

[0093] (3) The precipitate obtained in step (2) is mixed with lithium fluoride and a solvent by heating and stirring at 60-80° C. to obtain a mixed slurry with a solid content of 20-30%, wherein the mass ratio of the precipitate obtained in step (2) to lithium fluoride in the mixed slurry is 1:(0.01-0.02); the obtained mixed slurry is then heated to 400-500° C. at a heating rate of 5-8° C. / min and kept warm for 1-2 hours, and then heated to 500-600° C. at a heating rate of 4-6° C. / min and kept warm for 2-3 hours to obtain a positive electrode precursor.

[0094] In a third aspect, the present invention provides a positive electrode material, which is prepared from the positive electrode precursor described in the first aspect.

[0095] In a fourth aspect, the present invention provides a method for preparing the positive electrode material according to the third aspect, the preparation method comprising:

[0096] The lithium source is mixed with the positive electrode precursor described in the first aspect and then sintered to obtain the positive electrode material.

[0097] Preferably, the lithium source comprises lithium hydroxide and / or lithium carbonate.

[0098] Preferably, the mass ratio of the lithium source to the positive electrode material in the mixture is 1:(1-1.1), for example, it can be 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09 or 1:1.1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0099] Preferably, the sintering temperature is 750-900° C. and the sintering time is 10-15 hours.

[0100] In the present invention, the sintering temperature is 750-900°C, for example, it can be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C or 900°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0101] In the present invention, the sintering time is 10 to 15 hours, for example, it can be 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0102] In a fourth aspect, the present invention provides a battery comprising the positive electrode material described in the third aspect.

[0103] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0104] Compared with the prior art, the present invention has the following beneficial effects:

[0105] (1) In the positive electrode precursor provided by the present invention, boron is doped in both the boron-doped ternary material core and the boron-doped ternary material layer. Since the boron element has a small ionic radius, it is embedded in the crystal lattice to form a BO bond with a high bond energy, which effectively enhances the rigidity of the crystal structure and inhibits oxygen loss and phase change at high temperatures, thereby enhancing the structural stability and thermal stability of the positive electrode precursor and the positive electrode material prepared using the positive electrode precursor. In addition, boron doping also reduces the accumulation of lattice stress in the positive electrode precursor, further improving the structural stability of the positive electrode precursor and the positive electrode material prepared using the positive electrode precursor.

[0106] (2) In the positive electrode precursor provided by the present invention, the mass fraction of the boron element in the boron-doped ternary material core is lower than the mass fraction of the boron element in the boron-doped ternary material layer. The boron-doped ternary material core has a lower boron concentration. While maintaining the lattice integrity of the boron-doped ternary material core, it avoids the obstruction of lithium diffusion caused by excessive doping, thereby ensuring that the positive electrode material prepared with the positive electrode precursor has good electrochemical properties; the boron-doped ternary material layer has a higher boron concentration, which improves the structural stability and thermal stability of the boron-doped ternary material layer, strengthens the surface and interface structure of the positive electrode precursor, and inhibits the expansion of cracks from the surface to the inside of the positive electrode precursor, thereby improving the structural stability of the positive electrode precursor. BRIEF DESCRIPTION OF THE DRAWINGS

[0107] Figure 1 This is the EMPA diagram of the boron gradient-doped positive electrode precursor in Example 1. DETAILED DESCRIPTION

[0108] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0109] Example 1

[0110] This embodiment provides a boron-gradient-doped cathode precursor, comprising a boron-doped ternary material core having a D50 particle size of 3.5 μm, a boron-doped ternary material layer having a thickness of 5.5 μm coated on the outside of the boron-doped ternary material core, and a lithium fluoride coating layer having a thickness of 120 nm coated on the outside of the boron-doped ternary material layer;

[0111] Taking the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of the boron element in the boron-doped ternary material core is 0.8 wt %;

[0112] Based on the mass fraction of the boron-doped ternary material layer being 100%, the mass fraction of the boron element in the boron-doped ternary material layer is 2.2 wt %;

[0113] A gradient transition region with a thickness of 350 nm is further provided between the boron-doped ternary material core and the boron-doped ternary material layer; in the gradient transition region, the boron content increases linearly from the direction close to the boron-doped ternary material core to the direction close to the boron-doped ternary material layer;

[0114] A BOF bonding transition layer with a thickness of 500 nm is also included between the boron-doped ternary material layer and the lithium fluoride coating layer;

[0115] The boron gradient doped cathode precursor provided in this embodiment was tested using electron probe microanalysis technology, and the EMPA diagram of the cathode precursor was obtained as shown in FIG. Figure 1 shown.

[0116] The preparation method of the positive electrode precursor comprises:

[0117] (1) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 95:4:1), adding the metal mixed salt solution, precipitant solution, complexing agent solution and boric acid solution to a reaction base liquid in parallel to form a reaction solution, controlling the pH value of the reaction solution to 9.5, the ammonia concentration to 2.5 g / L, the boron concentration to 1500 ppm and the temperature to 60° C., and stirring at a speed of 600 rpm, and performing a first coprecipitation reaction in the reaction solution to obtain a solution containing a boron-doped ternary material core;

[0118] (2) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 95:4:1), adding the metal mixed salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution, controlling the pH value of the reaction solution to 11.5, the ammonia concentration to 6 g / L, the boron concentration to 3000 ppm and the temperature to 60° C., stirring at a speed of 600 rpm, performing a second coprecipitation reaction in the reaction solution, filtering, and then washing the obtained solid with alkali and water in sequence, and then drying at 120° C. to obtain a precipitate;

[0119] The ratio of the time of the first coprecipitation reaction in step (1) to the time of the second coprecipitation reaction in step (2) is 1:1.5;

[0120] (3) The precipitate obtained in step (2) is mixed with lithium fluoride and a solvent by heating and stirring at 70° C. to obtain a mixed slurry with a solid content of 25%, wherein the mass ratio of the precipitate obtained in step (2) to lithium fluoride in the mixed slurry is 1:0.015; the obtained mixed slurry is then heated to 450° C. at a heating rate of 6.5° C. / min and kept warm for 1.5 h, and then heated to 550° C. at a heating rate of 5° C. / min and kept warm for 2.5 h to obtain a positive electrode precursor.

[0121] Example 2

[0122] This embodiment provides a boron gradient-doped positive electrode precursor, comprising a boron-doped ternary material core having a D50 particle size of 2 μm, a boron-doped ternary material layer having a thickness of 7 μm coated on the outside of the boron-doped ternary material core, and a lithium fluoride coating layer having a thickness of 50 nm coated on the outside of the boron-doped ternary material layer;

[0123] Taking the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of the boron element in the boron-doped ternary material core is 0.1 wt %;

[0124] Taking the mass fraction of the boron-doped ternary material layer as 100%, the mass fraction of the boron element in the boron-doped ternary material layer is 1.5 wt %;

[0125] A gradient transition region with a thickness of 500 nm is further provided between the boron-doped ternary material core and the boron-doped ternary material layer; in the gradient transition region, the boron content increases linearly from the direction close to the boron-doped ternary material core to the direction close to the boron-doped ternary material layer;

[0126] A BOF bonding transition layer with a thickness of 200 nm is further included between the boron-doped ternary material layer and the lithium fluoride coating layer;

[0127] The preparation method of the positive electrode precursor comprises:

[0128] (1) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 98:1:1), adding the metal mixed salt solution, precipitant solution, complexing agent solution and boric acid solution to a reaction base liquid in parallel to form a reaction solution, controlling the pH value of the reaction solution to 9.0, the ammonia concentration to 2 g / L, the boron concentration to 1200 ppm and the temperature to 65° C., and stirring at a speed of 650 rpm, and performing a first coprecipitation reaction in the reaction solution to obtain a solution containing a boron-doped ternary material core;

[0129] (2) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 98:1:1), adding the metal mixed salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution, controlling the pH value of the reaction solution to 12.0, the ammonia concentration to 7 g / L, the boron concentration to 2700 ppm and the temperature to 65° C., stirring at a speed of 650 rpm, performing a second coprecipitation reaction in the reaction solution, filtering, and then washing the obtained solid with alkali and water in sequence, and then drying at 80° C. to obtain a precipitate;

[0130] The ratio of the time of the first coprecipitation reaction in step (1) to the time of the second coprecipitation reaction in step (2) is 1:2;

[0131] (3) The precipitate obtained in step (2) is mixed with lithium fluoride and a solvent by heating and stirring at 60° C. to obtain a mixed slurry with a solid content of 20%, wherein the mass ratio of the precipitate obtained in step (2) to lithium fluoride in the mixed slurry is 1:0.01; the obtained mixed slurry is then heated to 400° C. at a heating rate of 5° C. / min and kept warm for 2 h, and then heated to 500° C. at a heating rate of 4° C. / min and kept warm for 3 h to obtain a positive electrode precursor.

[0132] Example 3

[0133] This embodiment provides a boron-gradient-doped positive electrode precursor, comprising a boron-doped ternary material core having a D50 particle size of 5 μm, a boron-doped ternary material layer having a thickness of 4 μm coated on the outside of the boron-doped ternary material core, and a lithium fluoride coating layer having a thickness of 300 nm coated on the outside of the boron-doped ternary material layer;

[0134] Taking the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of the boron element in the boron-doped ternary material core is 1.5 wt %;

[0135] Taking the mass fraction of the boron-doped ternary material layer as 100%, the mass fraction of the boron element in the boron-doped ternary material layer is 3 wt %;

[0136] A gradient transition region with a thickness of 200 nm is further provided between the boron-doped ternary material core and the boron-doped ternary material layer; in the gradient transition region, the boron content increases linearly from the direction close to the boron-doped ternary material core to the direction close to the boron-doped ternary material layer;

[0137] A BOF bonding transition layer with a thickness of 200 nm is further included between the boron-doped ternary material layer and the lithium fluoride coating layer;

[0138] The preparation method of the positive electrode precursor comprises:

[0139] (1) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 96:2:2), adding the metal mixed salt solution, precipitant solution, complexing agent solution and boric acid solution to a reaction base liquid in parallel to form a reaction solution, controlling the pH value of the reaction solution to 10.0, the ammonia concentration to 3 g / L, the boron concentration to 1800 ppm and the temperature to 55° C., and stirring at a speed of 550 rpm, and performing a first coprecipitation reaction in the reaction solution to obtain a solution containing a boron-doped ternary material core;

[0140] (2) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 96:2:2), adding the metal mixed salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution, controlling the pH value of the reaction solution to 11.0, the ammonia concentration to 5 g / L, the boron concentration to 3300 ppm and the temperature to 55° C., stirring at a speed of 550 rpm, performing a second coprecipitation reaction in the reaction solution, filtering, and then washing the obtained solid with alkali and water in sequence, and then drying at 160° C. to obtain a precipitate;

[0141] The ratio of the time of the first coprecipitation reaction in step (1) to the time of the second coprecipitation reaction in step (2) is 1:1;

[0142] (3) The precipitate obtained in step (2) is mixed with lithium fluoride and a solvent by heating and stirring at 80° C. to obtain a mixed slurry with a solid content of 30%, wherein the mass ratio of the precipitate obtained in step (2) to lithium fluoride in the mixed slurry is 1:0.02; the obtained mixed slurry is then heated to 500° C. at a heating rate of 8° C. / min and kept warm for 1 hour, and then heated to 600° C. at a heating rate of 4° C. / min and kept warm for 2 hours to obtain a positive electrode precursor.

[0143] Example 4

[0144] This embodiment provides a boron gradient doped positive electrode precursor, divided by the mass fraction of the boron doped ternary material core as a percentage, the mass fraction of the boron element in the boron doped ternary material core is 0.02wt%;

[0145] That is, except that the concentration of boron element in the reaction solution in step (1) of the method for preparing the positive electrode precursor is 240 ppm, the rest is the same as in Example 1.

[0146] Example 5

[0147] This embodiment provides a boron gradient doped positive electrode precursor, divided by the mass fraction of the boron doped ternary material core as a percentage, the mass fraction of the boron element in the boron doped ternary material core is 2wt%;

[0148] That is, except that the concentration of the boron element in the reaction solution in step (1) of the method for preparing the positive electrode precursor is 3000 ppm, the rest is the same as in Example 1.

[0149] Example 6

[0150] This embodiment provides a boron gradient doped positive electrode precursor, divided by the mass fraction of the boron doped ternary material layer, the mass fraction of the boron element in the boron doped ternary material layer is 1 wt %;

[0151] That is, except that the concentration of the boron element in the reaction solution in step (2) of the method for preparing the positive electrode precursor is 1500 ppm, the rest is the same as in Example 1.

[0152] Example 7

[0153] This embodiment provides a boron gradient doped positive electrode precursor, divided by the mass fraction of the boron doped ternary material layer, the mass fraction of the boron element in the boron doped ternary material layer is 5wt%;

[0154] That is, except that the concentration of the boron element in the reaction solution in step (2) of the method for preparing the positive electrode precursor is 4500 ppm, the rest is the same as in Example 1.

[0155] Example 8

[0156] This embodiment provides a boron gradient doped cathode precursor, except that the BOF bonding transition layer is omitted;

[0157] That is, in step (3) of the method for preparing the positive electrode precursor, "then heating the obtained mixed slurry to 450°C at a heating rate of 6.5°C / min and keeping it warm for 1.5 hours, and then heating it to 550°C at a heating rate of 5°C / min and keeping it warm for 2.5 hours to obtain a positive electrode precursor" is replaced by "then vacuum drying the obtained mixed slurry at 90°C to obtain a positive electrode precursor", and the rest are the same as Example 1.

[0158] Comparative Example 1

[0159] This comparative example provides a boron-gradient-doped positive electrode precursor, in which the mass fraction of the boron element in the boron-doped ternary material core and the mass fraction of the boron element in the boron-doped ternary material layer are both 0.8 wt %, and there is no gradient transition zone between the boron-doped ternary material core and the boron-doped ternary material layer;

[0160] That is, except that the concentration of the boron element in the reaction solution in step (2) of the method for preparing the positive electrode precursor is 1500 ppm, the rest is the same as in Example 1.

[0161] Comparative Example 2

[0162] This comparative example provides a boron-gradient-doped positive electrode precursor, in which the mass fraction of the boron element in the boron-doped ternary material core and the mass fraction of the boron element in the boron-doped ternary material layer are both 2.2 wt %, and there is no gradient transition zone between the boron-doped ternary material core and the boron-doped ternary material layer;

[0163] That is, except that the concentration of the boron element in the reaction solution in step (1) of the method for preparing the positive electrode precursor is 3000 ppm, the rest is the same as in Example 1.

[0164] Comparative Example 3

[0165] This comparative example provides a boron gradient-doped positive electrode precursor, in which the mass fraction of the boron element in the boron-doped ternary material core is greater than the mass fraction of the boron element in the boron-doped ternary material layer, and in the gradient transition region, the boron content decreases linearly from the direction close to the boron-doped ternary material core to the direction close to the boron-doped ternary material layer;

[0166] Taking the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of the boron element in the boron-doped ternary material core is 2.2 wt %;

[0167] Taking the mass fraction of the boron-doped ternary material layer as 100%, the mass fraction of the boron element in the boron-doped ternary material layer is 0.8 wt %;

[0168] That is, the preparation method of the positive electrode precursor is the same as that of Example 1 except that the concentration of boron in the reaction solution in step (1) is 3000 ppm and the concentration of boron in the reaction solution in step (2) is 1500 ppm.

[0169] Comparative Example 4

[0170] This comparative example provides a boron gradient-doped positive electrode precursor, in which the boron-doped ternary material core is replaced by a ternary material core that is not doped with boron, and the boron-doped ternary material layer is replaced by a ternary material layer that is not doped with boron, and there is no gradient transition zone between the boron-doped ternary material core and the boron-doped ternary material layer;

[0171] That is, except for omitting the boron element in the reaction solution in step (1) and step (2) of the method for preparing the positive electrode precursor, the rest is the same as in Example 1.

[0172] The positive electrode precursor provided in the above embodiment and comparative example is mixed with lithium carbonate, and the mass ratio of the positive electrode precursor to lithium carbonate is 1:1.05, and then sintered at 850°C for 12 hours to obtain a positive electrode material; the obtained positive electrode material is then mixed with conductive carbon black and polyvinylidene fluoride in a mass ratio of 90:5:5, and N-methylpyrrolidone is used as the solvent, and the mixture is stirred into a slurry; the obtained slurry is evenly coated on an aluminum foil with a scraper with a coating gap of 100 μm; after coating, it is first blown dry, and then rolled and cut into circular electrode sheets, and then vacuum dried at 120°C and the weight of the electrode sheets is weighed to obtain a button half-cell positive electrode sheet; a metal lithium sheet is selected as the negative electrode, a PP microporous membrane is selected as the diaphragm, and a lithium battery basic electrolyte is selected as the electrolyte. The positive electrode sheet, the metal lithium sheet, the diaphragm and the electrolyte are assembled to obtain a button battery.

[0173] The electrochemical performance of the button cell was tested at a rate of 5C at a voltage range of 2.8 to 4.3 V at 25°C. The first discharge specific capacity of the button cell obtained by the test is shown in Table 1.

[0174] The electrochemical performance of the button cell was tested at 25°C, within a voltage range of 2.8 to 4.3 V, and at a rate of 3C. The discharge capacity of the button cell obtained by the test is shown in Table 1.

[0175] The electrochemical performance of the button cell was tested at a rate of 1C at a voltage range of 2.8 to 4.3 V at 25°C. The capacity retention after 500 cycles is shown in Table 1.

[0176] A fully charged battery (e.g., 100% SOC) was placed in an insulated, sealed chamber with an initial temperature set at 50°C. The temperature was then increased in steps of 0.5°C. When a self-heating temperature rise rate of ≥0.02°C / min was detected, the adiabatic tracking mode was triggered, and the temperature and pressure changes were recorded in real time to obtain the thermal runaway onset temperature, as shown in Table 1. The thermal runaway onset temperature was defined as the inflection point of irreversible acceleration of self-heating (corresponding to a temperature rise rate of ≥1°C / min).

[0177] Table 1

[0178]

[0179] From Table 1 and Table 2, we can get:

[0180] (1) The battery containing the positive electrode material prepared by the boron gradient-doped positive electrode precursor provided in Examples 1 to 3 exhibits a higher discharge specific capacity and a higher capacity retention rate;

[0181] (2) By comparing Example 1 with Examples 4 and 5, it can be seen that in the present invention, the mass fraction of the boron element in the core of the boron-doped ternary material is 100%, and the mass fraction of the boron element in the core of the boron-doped ternary material will affect the performance of the positive electrode precursor, the positive electrode material and the battery; when the mass fraction of the boron element in the core of the boron-doped ternary material is 0.1-1.5wt%, the positive electrode precursor and the positive electrode material have better performance. This is because when the mass fraction of the boron element in the core of the boron-doped ternary material is 0.1-1.5wt%, a strong BO bond is formed by embedding an appropriate amount of boron element into the crystal lattice, thereby enhancing the rigidity of the core crystal structure, inhibiting cation mixing and high-temperature oxygen loss, and avoiding the obstruction of lithium ion diffusion caused by excessive doping, thereby maintaining the integrity of the lattice; the low boron concentration in the core and the high boron in the outer layer are connected through a gradient transition zone, so that the boron content changes linearly, reducing the stress concentration caused by lattice mutation, and synergistically inhibiting the expansion of bulk cracks;

[0182] (3) By comparing Example 1 with Examples 6 and 7, it can be seen that in the present invention, the mass fraction of the boron element in the boron-doped ternary material layer is 100%, and the mass fraction of the boron element in the boron-doped ternary material layer will affect the performance of the positive electrode precursor and the positive electrode material; when the mass fraction of the boron element in the boron-doped ternary material layer is 1.5-3wt%, the positive electrode precursor and the positive electrode material have better performance. This is because the boron content range can not only enhance the synergistic effect of the boron-doped ternary material layer and the lithium fluoride coating layer, forming a stable BOF bonded transition layer to inhibit electrolyte corrosion and transition metal dissolution, but also avoid the blockage of the lithium ion transmission channel caused by excessive boron enrichment, thereby balancing the structural stability and electrochemical kinetic performance of the material;

[0183] (4) By comparing Example 1 with Example 8, it can be seen that in the present invention, the lithium fluoride in the lithium fluoride coating layer reacts with the boron in the boron-doped ternary material layer to form a BOF bonded transition layer with a thermal decomposition temperature higher than 400°C. The BOF bonded transition layer has both high ionic conductivity and strong chemical bonding, which not only relieves the lattice stress caused by volume change during charging and discharging, but also inhibits oxygen release and phase change heat release at high temperature through the strong covalency of the BOF bond, thereby synergistically enhancing the structural stability and thermal stability of the positive electrode precursor;

[0184] (5) By comparing Example 1 with Comparative Examples 1 to 4, it can be seen that in the positive electrode precursor provided by the present invention, boron is doped in both the boron-doped ternary material core and the boron-doped ternary material layer. Since the boron element has a small ionic radius, it is embedded in the crystal lattice to form a BO bond with a high bond energy, which effectively enhances the rigidity of the crystal structure and inhibits oxygen loss and phase change at high temperatures, thereby enhancing the structural stability and thermal stability of the positive electrode precursor and the positive electrode material prepared using the positive electrode precursor; in addition, boron doping also reduces the lattice stress accumulation in the positive electrode precursor, further improving the structural stability of the positive electrode precursor and the positive electrode material prepared using the positive electrode precursor;

[0185] In the positive electrode precursor provided by the present invention, the mass fraction of the boron element in the boron-doped ternary material core is lower than the mass fraction of the boron element in the boron-doped ternary material layer. The boron-doped ternary material core has a lower boron concentration. While maintaining the lattice integrity of the boron-doped ternary material core, it avoids the obstruction of lithium diffusion caused by excessive doping, thereby ensuring that the positive electrode material prepared with the positive electrode precursor has good electrochemical properties; the boron-doped ternary material layer has a higher boron concentration, which improves the structural stability and thermal stability of the boron-doped ternary material layer, strengthens the surface and interface structure of the positive electrode precursor, and inhibits the expansion of cracks from the surface to the inside of the positive electrode precursor, thereby improving the structural stability of the positive electrode precursor.

[0186] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A boron gradient doped cathode precursor, characterized in that: The positive electrode precursor includes a boron-doped ternary material core and a boron-doped ternary material layer coated on the outside of the boron-doped ternary material core; The mass fraction of the boron element in the boron-doped ternary material core is lower than the mass fraction of the boron element in the boron-doped ternary material layer.

2. The cathode precursor according to claim 1, characterized in that Taking the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of the boron element in the boron-doped ternary material core is 0.1-1.5 wt %; Preferably, based on the mass fraction of the boron-doped ternary material layer as 100%, the mass fraction of the boron element in the boron-doped ternary material layer is 1.5-3 wt %; Preferably, a gradient transition zone is further included between the boron-doped ternary material core and the boron-doped ternary material layer; In the gradient transition region, the boron content increases linearly from the direction close to the boron-doped ternary material core to the direction close to the boron-doped ternary material layer; Preferably, the thickness of the gradient transition zone is 200-500 nm.

3. The cathode precursor according to claim 1, characterized in that The positive electrode precursor further includes a lithium fluoride coating layer coated on the outside of the boron-doped ternary material layer.

4. The cathode precursor according to claim 3, characterized in that A BOF bonding transition layer is further included between the boron-doped ternary material layer and the lithium fluoride coating layer; Preferably, the thickness of the BOF bonding transition layer is 200-800 nm.

5. A method for preparing the positive electrode precursor according to any one of claims 1 to 4, characterized in that: The preparation method comprises: (1) adding a metal mixed salt solution, a precipitant solution, a complexing agent solution and a boron source to a reaction base liquid in parallel to form a reaction solution, and performing a first coprecipitation reaction in the reaction solution to obtain a solution containing a boron-doped ternary material core; (2) adding the metal mixed salt solution, the precipitant solution, the complexing agent solution and the boron source in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution, and performing a second coprecipitation reaction in the reaction solution to obtain a positive electrode precursor; The concentration of the boron source in the reaction solution of step (1) is less than the concentration of the boron source in the reaction solution of step (2).

6. The preparation method according to claim 5, characterized in that In the first coprecipitation reaction of step (1), the pH value of the reaction solution is controlled to be 9.0-10.0; Preferably, in the first coprecipitation reaction in step (1), the ammonia concentration in the reaction solution is controlled to be 2-3 g / L; Preferably, in the first coprecipitation reaction of step (1), the concentration of boron in the reaction solution is controlled to be 1200 to 1800 ppm; Preferably, the time ratio of the first coprecipitation reaction in step (1) to the second coprecipitation reaction in step (2) is 1:(1-2); Preferably, in the second coprecipitation reaction in step (2), the pH value of the reaction solution is controlled to be 11.0-12.0; Preferably, in the second coprecipitation reaction in step (2), the ammonia concentration in the reaction solution is controlled to be 5 to 7 g / L; Preferably, in the second coprecipitation reaction in step (2), the concentration of boron in the reaction solution is controlled to be 2700-3300 ppm.

7. The preparation method according to claim 5 or 6, characterized in that: The preparation method further comprises step (2) after the second coprecipitation reaction: mixing the precipitate obtained by the second coprecipitation reaction, lithium fluoride and a solvent to obtain a mixed slurry, and then heat-treating the obtained mixed slurry to obtain a positive electrode precursor; Preferably, the mass ratio of the precipitate obtained by the second coprecipitation reaction to lithium fluoride in the mixing is 1:(0.01-0.02); Preferably, the solid content of the mixed slurry is 20-30%; Preferably, the heat treatment includes a first heating, a first heat preservation, a second heating and a second heat preservation performed in sequence; Preferably, the first heating rate is 5-8°C / min, and the end temperature is 400-500°C; Preferably, the first insulation time is 1 to 2 hours; Preferably, the heating rate of the second heating is 4-6°C / min, and the end temperature is 500-600°C; Preferably, the first insulation time is 2 to 3 hours.

8. The preparation method according to claim 5, characterized in that The preparation method comprises: (1) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution, adding the metal mixed salt solution, precipitant solution, complexing agent solution and boric acid solution to a reaction base liquid in parallel to form a reaction solution, controlling the pH value of the reaction solution to 9.0-10.0, the ammonia concentration to 2-3 g / L, the boron concentration to 1200-1800 ppm and the temperature to 55-65° C., and stirring at a speed of 550-650 rpm to perform a first coprecipitation reaction in the reaction solution to obtain a solution containing a boron-doped ternary material core; (2) adding nickel salt, cobalt salt and manganese salt to a solvent to obtain a metal mixed salt solution, adding the metal mixed salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution, controlling the pH value of the reaction solution to 11.0-12.0, the ammonia concentration to 5-7 g / L, the boron concentration to 2700-3300 ppm and the temperature to 55-65° C., stirring at a speed of 550-650 rpm, carrying out a second coprecipitation reaction in the reaction solution, filtering, and sequentially washing the obtained solid with alkali and water, and then drying at 80-160° C. to obtain a precipitate; The ratio of the time of the first coprecipitation reaction in step (1) to the time of the second coprecipitation reaction in step (2) is 1:(1-2); (3) The precipitate obtained in step (2) is mixed with lithium fluoride and a solvent by heating and stirring at 60-80° C. to obtain a mixed slurry with a solid content of 20-30%, wherein the mass ratio of the precipitate obtained in step (2) to lithium fluoride in the mixed slurry is 1:(0.01-0.02); the obtained mixed slurry is then heated to 400-500° C. at a heating rate of 5-8° C. / min and kept warm for 1-2 hours, and then heated to 500-600° C. at a heating rate of 4-6° C. / min and kept warm for 2-3 hours to obtain a positive electrode precursor.

9. A positive electrode material, characterized in that The positive electrode material is prepared from the positive electrode precursor according to any one of claims 1 to 4.

10. A battery, characterized in that: The battery comprises the positive electrode material according to claim 9.

Images