Boron gradient doped cathode precursor, preparation method thereof, cathode material and battery

Abstract

The application provides a boron gradient doped positive electrode precursor, a preparation method of the positive electrode precursor, a positive electrode material and a battery, the positive electrode precursor comprises a boron doped ternary material inner core and a boron doped ternary material layer coated outside the boron doped ternary material inner core; the mass fraction of boron in the boron doped ternary material inner core is lower than the mass fraction of boron in the boron doped ternary material layer. In the boron gradient doped positive electrode precursor, boron is doped in the boron doped ternary material inner core and the boron doped ternary material layer, a B-O bond with high bond energy is formed, and the accumulation of lattice stress in the positive electrode precursor is reduced, so that the structural stability and thermal stability of the positive electrode precursor and the positive electrode material are improved; in addition, through the gradient doping of boron, the electrochemical performance of the positive electrode material is ensured, the surface 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] This invention belongs to the field of battery technology, and relates to boron gradient-doped cathode precursors, and more particularly to boron gradient-doped cathode precursors and their preparation methods, cathode materials and batteries. Background Technology

[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 many challenges in practical applications.

[0003] First, the nickel-cobalt-manganese ternary cathode materials disclosed in the prior art suffer from insufficient structural stability: ternary materials with high nickel content (Ni≥60%) exhibit severe structural degradation during charge and discharge, mainly manifested as cation mixing (Ni... 2+ Occupy Li + Crystal structure distortion caused by the site, and lattice stress caused by irreversible phase transition (H2→H3 phase transition) during cycling, lead to microcracks inside the material particles, which accelerates capacity decay.

[0004] Secondly, the nickel-cobalt-manganese ternary cathode materials disclosed in the existing technology also have potential thermal safety hazards: under high charge state (delithiation state), the crystal structure of the nickel-cobalt-manganese ternary cathode material is unstable, and oxygen atoms in the material lattice react with transition metals (especially Ni with high nickel content). 3+ / Ni 4+ The bonding strength of ) is significantly reduced, and the lattice oxygen (O) 2- It is easily released in the form of O2. The released oxygen reacts violently with the organic solvent in the electrolyte, releasing a large amount of heat, which leads to potential thermal safety hazards.

[0005] Due to the defects in nickel-cobalt-manganese ternary cathode materials, various methods are used in existing technologies to modify them. These methods mainly include: First, bulk doping, which involves uniform doping with elements such as Al, Mg, and Ti, partially suppressing cation mixing, but the modification effect is limited. Second, uniform doping with boron. 3+ With a small ionic radius, it is easy to enter the crystal lattice and form strong BO bonds, which can stabilize the crystal structure. However, uniform doping with boron still cannot effectively improve the structural and thermal stability of ternary cathode materials.

[0006] CN117766706A discloses a boron-doped diamond-coated high-power, long-cycle ternary cathode material and its preparation method. The preparation method includes the following steps: S1, the ternary cathode material is crushed and dispersed in a diamond suspension, crystallized under ultrasonic conditions, filtered, and dried to obtain a ternary cathode material with diamond seed crystals; S2, the ternary cathode material with diamond seed crystals is placed in a chemical vapor deposition apparatus, and deposition is performed 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 ternary cathode material, its preparation method, and its application. The preparation method of the Co-gradient doped ternary cathode material provided in this disclosure includes the following steps: 1) mixing a nickel-cobalt precursor, a lithium source, a cobalt source, an aluminum source, and a dopant metal compound to obtain a mixture; 2) sintering the mixture from step 1) in one step to obtain the Co-gradient doped ternary cathode material. However, modifying ternary cathode materials through Co-gradient doping 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 are still insufficient to effectively improve their structural and thermal stability. Therefore, it is crucial to develop and design a novel boron-gradient-doped cathode precursor and its preparation method, as well as cathode materials and batteries. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a boron gradient-doped cathode precursor, its preparation method, cathode material, and battery. In the boron gradient-doped cathode precursor provided by the present invention, boron doping is performed in both the boron-doped ternary material core and the boron-doped ternary material layer, forming high-energy BO bonds and reducing lattice stress accumulation in the cathode precursor. This improves the structural and thermal stability of the cathode precursor and the cathode material prepared from the cathode precursor. Furthermore, through boron gradient doping, while ensuring the electrochemical performance of the cathode material, the surface and interface structure of the cathode precursor is strengthened, suppressing crack propagation from the surface to the interior of the cathode precursor, and enhancing the structural stability of the cathode precursor.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[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 covering the boron-doped ternary material core.

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

[0013] In the cathode precursor provided by this invention, both the boron-doped ternary material core and the boron-doped ternary material layer are boron-doped. Due to the small ionic radius of boron, it is embedded in the crystal lattice to form BO bonds with high bond energy, which effectively enhances the rigidity of the crystal structure and suppresses oxygen loss and phase transition at high temperatures, thereby enhancing the structural and thermal stability of the cathode precursor and the cathode material prepared from the cathode precursor. In addition, boron doping also reduces the accumulation of lattice stress in the cathode precursor, further improving the structural stability of the cathode precursor and the cathode material prepared from the cathode precursor.

[0014] In the cathode precursor provided by this invention, the mass fraction of boron in the boron-doped ternary material core is lower than that in the boron-doped ternary material layer. The boron-doped ternary material core has a lower boron concentration, which maintains the lattice integrity of the boron-doped ternary material core while avoiding lithium diffusion obstruction caused by excessive doping, thus ensuring that the cathode material prepared from the cathode precursor has good electrochemical performance. The boron-doped ternary material layer has a higher boron concentration, which improves the structural and thermal stability of the boron-doped ternary material layer, strengthens the surface and interface structure of the cathode precursor, and inhibits crack propagation from the surface of the cathode precursor to the interior, thereby improving the structural stability of the cathode precursor.

[0015] In summary, the boron gradient-doped cathode precursor provided by this invention incorporates boron doping in both the boron-doped ternary material core and the boron-doped ternary material layer, forming high-energy BO bonds and reducing lattice stress accumulation in the cathode precursor. This enhances the structural and thermal stability of the cathode precursor and the cathode material prepared from it. Furthermore, the boron gradient doping ensures the electrochemical performance of the cathode material while strengthening the surface and interface structure of the cathode precursor, suppressing crack propagation from the surface to the interior of the cathode precursor, and improving the structural stability of the cathode precursor.

[0016] Preferably, taking the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of boron 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; other unlisted values ​​within this range are also applicable.

[0017] In this invention, when the mass fraction of boron in the core of the boron-doped ternary material is 0.1–1.5 wt%, the cathode precursor and cathode material exhibit superior performance. This is because when the mass fraction of boron in the core of the boron-doped ternary material is 0.1–1.5 wt%, strong BO bonds are formed by the appropriate amount of boron embedded in the crystal lattice, which enhances the rigidity of the core crystal structure, suppresses cation mixing and high-temperature oxygen loss, and avoids lithium-ion diffusion obstruction caused by excessive doping, thus maintaining lattice integrity. The low boron concentration in the core and the high boron concentration in the outer layer are connected through a gradient transition region, which makes the boron content change linearly, reduces stress concentration caused by lattice abrupt changes, and synergistically suppresses 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, other unlisted values ​​within this range are also applicable.

[0019] Preferably, the mass fraction of boron in the boron-doped ternary material layer is 1.5 to 3 wt%, based on the mass fraction of the boron doped ternary material layer. 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] In this invention, when the mass fraction of boron in the boron-doped ternary material layer is 1.5–3 wt%, the cathode precursor and cathode material exhibit superior performance. This is because this boron content range can both 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 suppress electrolyte erosion and transition metal dissolution, and avoid the blockage of lithium-ion transport channels caused by excessive boron enrichment, thus balancing the structural stability and electrochemical kinetic performance of the material.

[0021] Preferably, the thickness of the boron-doped ternary material layer is 4–7 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, other unlisted values ​​within this range are also applicable.

[0022] Preferably, a gradient transition region 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 near the boron-doped ternary material core to the direction near the boron-doped ternary material layer.

[0024] In this invention, a gradient transition region exists between the boron-doped ternary material core and the boron-doped ternary material layer. This gradient transition region not only acts as a buffer layer between the boron-doped ternary material core and the boron-doped ternary material layer, thereby absorbing the stress between them, but also allows for a gradient change in boron content between the boron-doped ternary material core, the gradient transition region, and the boron-doped ternary material layer. This reduces lattice abrupt changes, suppresses crack propagation, and thus improves the structural stability of the cathode precursor and the cathode material prepared from the cathode precursor.

[0025] Preferably, the thickness of the gradient transition region is 200–500 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, other unlisted values ​​within this range are also applicable.

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

[0027] The nickel-cobalt-manganese ternary cathode materials disclosed in the prior art also have the problem of insufficient interface stability: the surface of the nickel-cobalt-manganese ternary cathode material is prone to side reactions with the electrolyte, forming an unstable CEI film. In addition, the transition metal ions in the nickel-cobalt-manganese ternary cathode material are easy to dissolve in the electrolyte, which leads to the degradation of battery performance.

[0028] In this invention, the lithium fluoride coating can physically isolate the cathode material prepared from the cathode precursor from direct contact with the electrolyte, inhibit the erosion of electrolyte decomposition products, and reduce surface side reactions and transition metal dissolution, thereby improving the interfacial structural stability of the cathode material prepared from the cathode precursor and thus improving the electrochemical performance of the battery containing the cathode material.

[0029] Preferably, the thickness of the lithium fluoride coating 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 it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

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

[0031] In this invention, lithium fluoride in the lithium fluoride coating layer reacts with 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 alleviates the lattice stress caused by volume changes during charging and discharging, but also suppresses oxygen release and phase transition exothermics at high temperatures through the strong covalent nature of the BOF bonds, thus synergistically enhancing the structural and thermal stability of the cathode precursor.

[0032] Preferably, the thickness of the BOF bonding transition layer is 200–800 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, other unlisted values ​​within this range are also applicable.

[0033] In this invention, when the thickness of the BOF bonding transition layer is 200–800 nm, the cathode precursor and cathode material exhibit superior performance. This is because this thickness range can form a continuous and dense BOF bonding interface layer, which can effectively suppress oxygen release and phase transition exothermics at high temperatures through strong covalent bond interactions, while maintaining a fast lithium-ion transport channel, thereby synergistically improving the electrochemical performance and thermal stability of the cathode material prepared from the cathode precursor.

[0034] Preferably, the mass fraction of boron in the positive electrode precursor is 0.1 to 3 wt%, based on the total mass of the positive electrode precursor. 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. Other unlisted values ​​within this 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] Where, 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 this 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. Other unlisted values ​​within this range are also applicable.

[0038] In this 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 unlisted values ​​within this range are also applicable.

[0039] In this 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 unlisted values ​​within this range are also applicable.

[0040] In this 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 unlisted values ​​within this range are also applicable.

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

[0042] (1) A metal mixed salt solution, a precipitant solution, a complexing agent solution and a boron source are added to the reaction base liquid in parallel to form a reaction solution. The first co-precipitation reaction occurs in the reaction solution to obtain a solution containing a boron-doped ternary material core.

[0043] (2) The metal mixed salt solution, precipitant solution, complexing agent solution and boron source are added in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution. The second coprecipitation reaction is carried out in the reaction solution to obtain the positive electrode precursor.

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

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

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

[0047] Preferably, the mass concentration of the precipitant in the precipitant solution described in steps (1) and (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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the complexing agent in the complexing agent solution described in steps (1) and (2) independently includes any one or a combination of at least two of ammonia, ethylenediaminetetraacetic acid, citric acid or oxalic acid. 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 described in steps (1) and (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 it is not limited to the listed values. Other unlisted values ​​within this 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 to 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 9.6 to 9.8.

[0051] Preferably, in the first coprecipitation reaction in 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 it is not limited to the listed values. Other unlisted values ​​within this 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 to 1800 ppm, for example, it can be 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm or 1800 ppm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

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

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

[0055] In this invention, during the co-current addition process described in step (1), the concentration of boric acid in the added boric acid solution is 3.0 to 6.0 g / L, for example, it can be 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 3.6 to 5.4 g / L.

[0056] In this invention, during the co-current addition process described in step (1), the addition flow rate of 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 1.2 to 1.8 L / h.

[0057] Preferably, the borate includes sodium borate.

[0058] Preferably, the first coprecipitation reaction in step (1) is accompanied by stirring at a speed of 550 to 650 rpm, for example, 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 range are also applicable.

[0059] Preferably, in step (1) the first coprecipitation reaction, the temperature of the reaction solution is controlled at 55-65°C, for example, 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. Other unlisted values ​​within this 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0061] Preferably, in step (2) the second coprecipitation reaction, the pH value of the reaction solution is controlled to be 11.0 to 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 11.2 to 11.4.

[0062] Preferably, in step (2) the second coprecipitation reaction, the ammonia concentration in the reaction solution is controlled to be 5-7 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 5.5-6.5 g / L.

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

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

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

[0066] In this invention, during the co-current addition process described 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 8.2 to 10.8 g / L.

[0067] In this invention, during the co-current addition process described in step (2), the addition flow rate of 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 1.8 to 3.6 L / h.

[0068] Preferably, the borate includes sodium borate.

[0069] Preferably, the second coprecipitation reaction in step (2) is accompanied by stirring at a speed of 550 to 650 rpm, for example, 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 range are also applicable.

[0070] Preferably, in step (2) the second coprecipitation reaction, the temperature of the reaction solution is controlled at 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

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

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

[0073] Preferably, the mass ratio of the precipitate obtained from the second co-precipitation reaction in the mixture to lithium fluoride is 1:(0.01 to 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 it is not limited to the listed values. Other unlisted values ​​within this 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. Other unlisted values ​​within this 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, 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 range are also applicable.

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

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

[0078] In this 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0079] In this 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0080] Preferably, the first heat preservation 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

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

[0082] In this 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0083] In this 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0084] Preferably, the first heat preservation 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

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

[0086] Preferably, the washing process includes an alkaline wash followed by a water wash.

[0087] Preferably, the washing solution used in the alkaline washing process includes a NaOH solution with a mass fraction of 3-4 wt%, for example, it can be 3.0 wt%, 3.1 wt%, 3.2 wt%, 3.3 wt%, 3.4 wt%, 3.5 wt%, 3.6 wt%, 3.7 wt%, 3.8 wt%, 3.9 wt%, or 4.0 wt%, but is not limited to the listed values, other unlisted values ​​within this 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 120-160°C.

[0089] As a preferred embodiment of the preparation method of the present invention, the preparation method includes:

[0090] (1) Add nickel salt, cobalt salt and manganese salt to a solvent to obtain a mixed metal salt solution. Add the mixed metal salt solution, precipitant solution, complexing agent solution and boric acid solution in parallel to the reaction base liquid to form a reaction solution. Control the pH value of the reaction solution to 9.0-10.0, the ammonia concentration to 2-3 g / L, the boron element concentration to 1200-1800 ppm and the temperature to 55-65℃. Stir at a speed of 550-650 rpm. A first co-precipitation reaction is carried out in the reaction solution to obtain a solution containing a boron-doped ternary material core.

[0091] (2) Add nickel salt, cobalt salt and manganese salt to a solvent to obtain a mixed metal salt solution. Add the mixed metal salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing boron-doped ternary material core obtained in step (1) to form a reaction solution. Control the pH value of the reaction solution to 11.0-12.0, the ammonia concentration to 5-7 g / L, the boron element concentration to 2700-3300 ppm and the temperature to 55-65℃. Stir at a speed of 550-650 rpm to carry out the second coprecipitation reaction in the reaction solution. After filtration, the obtained solid is washed with alkali and water in sequence, and then dried at 80-160℃ to obtain the precipitate.

[0092] The time ratio of the first coprecipitation reaction in step (1) to 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 solvent by heating and stirring at 60-80°C to obtain a mixed slurry with a solid content of 20-30%. The mass ratio of the precipitate obtained in step (2) to lithium fluoride in the mixed slurry is 1:(0.01-0.02). The mixed slurry is then heated to 400-500°C at a heating rate of 5-8°C / min and held for 1-2 hours. Then, it is heated to 500-600°C at a heating rate of 4-6°C / min and held for 2-3 hours to obtain the positive electrode precursor.

[0094] Thirdly, the present invention provides a cathode material, which is prepared from the cathode precursor described in the first aspect.

[0095] Fourthly, the present invention provides a method for preparing the cathode material described in the third aspect, the method comprising:

[0096] After mixing the lithium source with the cathode precursor described in the first aspect, the mixture is sintered to obtain the cathode material.

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

[0098] Preferably, the mass ratio of lithium source to cathode material in the mixture is 1:(1 to 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

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

[0100] In this 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, other unlisted values ​​within this range are also applicable.

[0101] In this 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 it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

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

[0103] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all 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, both the boron-doped ternary material core and the boron-doped ternary material layer are boron-doped. Since boron has a small ionic radius, it is embedded in the lattice to form BO bonds with high bond energy, which effectively enhances the rigidity of the crystal structure and suppresses oxygen loss and phase transformation at high temperature, thereby enhancing the structural stability and thermal stability of the positive electrode precursor and the positive electrode material prepared from 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 from the positive electrode precursor.

[0106] (2) In the positive electrode precursor provided by the present invention, the mass fraction of boron in the boron-doped ternary material core is lower than that in the boron-doped ternary material layer. The boron-doped ternary material core has a lower boron concentration, which maintains the lattice integrity of the boron-doped ternary material core while avoiding the obstruction of lithium diffusion caused by excessive doping, thus ensuring that the positive electrode material prepared from the positive electrode precursor has good electrochemical performance. 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 propagation of cracks from the surface of the positive electrode precursor to the interior, thereby improving the structural stability of the positive electrode precursor. Attached Figure Description

[0107] Figure 1 This is an EMPA diagram of the boron gradient-doped cathode precursor in Example 1. Detailed Implementation

[0108] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0109] Example 1

[0110] This embodiment provides a boron gradient-doped cathode precursor, which includes a boron-doped ternary material core with a D50 particle size of 3.5 μm, a boron-doped ternary material layer with a thickness of 5.5 μm covering the boron-doped ternary material core, and a lithium fluoride coating layer with a thickness of 120 nm covering the boron-doped ternary material layer.

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

[0112] With the mass fraction of the boron-doped ternary material layer as 100%, the mass fraction of boron in the boron-doped ternary material layer is 2.2 wt%.

[0113] The boron-doped ternary material core and the boron-doped ternary material layer also include a gradient transition region with a thickness of 350 nm; in the gradient transition region, the boron content increases linearly from the direction near the boron-doped ternary material core to the direction near the boron-doped ternary material layer.

[0114] The boron-doped ternary material layer and the lithium fluoride coating layer also include a BOF bonding transition layer with a thickness of 500 nm.

[0115] The boron gradient-doped cathode precursor provided in this embodiment was tested using electron probe microanalysis (EPMA) technology, and the EMMA image of the cathode precursor is shown below. Figure 1 As shown.

[0116] The method for preparing the positive electrode precursor includes:

[0117] (1) Add nickel salt, cobalt salt and manganese salt to a solvent to obtain a mixed metal salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 95:4:1). Add the mixed metal salt solution, precipitant solution, complexing agent solution and boric acid solution in parallel to the reaction base liquid to form a reaction solution. Control the pH value of the reaction solution to 9.5, the ammonia concentration to 2.5 g / L, the boron element concentration to 1500 ppm and the temperature to 60℃. Stir at 600 rpm to carry out the first co-precipitation reaction in the reaction solution to obtain a solution containing a boron-doped ternary material core.

[0118] (2) Add nickel salt, cobalt salt and manganese salt to a solvent to obtain a mixed metal salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 95:4:1). Add the mixed metal salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing boron-doped ternary material core obtained in step (1) to form a reaction solution. Control the pH value of the reaction solution to 11.5, the ammonia concentration to 6g / L, the boron element concentration to 3000ppm and the temperature to 60℃. Stir at 600rpm to carry out the second coprecipitation reaction in the reaction solution. After filtration, the obtained solid is washed with alkali and water in sequence, and then dried at 120℃ to obtain the precipitate.

[0119] The time ratio of the first coprecipitation reaction in step (1) to 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 solvent by heating and stirring at 70°C to obtain a mixed slurry with a solid content of 25%. The mass ratio of the precipitate obtained in step (2) to lithium fluoride in the mixed slurry is 1:0.015. The mixed slurry is then heated to 450°C at a heating rate of 6.5°C / min and held for 1.5h. Then it is heated to 550°C at a heating rate of 5°C / min and held for 2.5h to obtain the positive electrode precursor.

[0121] Example 2

[0122] This embodiment provides a boron gradient-doped cathode precursor, which includes a boron-doped ternary material core with a D50 particle size of 2 μm, a boron-doped ternary material layer with a thickness of 7 μm covering the boron-doped ternary material core, and a lithium fluoride coating layer with a thickness of 50 nm covering the boron-doped ternary material layer.

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

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

[0125] The boron-doped ternary material core and the boron-doped ternary material layer also include a gradient transition region with a thickness of 500 nm; in the gradient transition region, the boron content increases linearly from the direction closer to the boron-doped ternary material core to the direction closer to the boron-doped ternary material layer.

[0126] The boron-doped ternary material layer and the lithium fluoride coating layer also include a BOF bonding transition layer with a thickness of 200 nm.

[0127] The method for preparing the positive electrode precursor includes:

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

[0129] (2) Add 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). Add the metal mixed salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing boron-doped ternary material core obtained in step (1) to form a reaction solution. Control the pH value of the reaction solution to 12.0, the ammonia concentration to 7g / L, the boron element concentration to 2700ppm and the temperature to 65℃. Stir at 650rpm to carry out the second coprecipitation reaction in the reaction solution. After filtration, the obtained solid is washed with alkali and water in sequence, and then dried at 80℃ to obtain the precipitate.

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

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

[0132] Example 3

[0133] This embodiment provides a boron gradient doped cathode precursor, which includes a boron-doped ternary material core with a D50 particle size of 5 μm, a boron-doped ternary material layer with a thickness of 4 μm covering the boron-doped ternary material core, and a lithium fluoride coating layer with a thickness of 300 nm covering the boron-doped ternary material layer.

[0134] With the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of boron 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 boron in the boron-doped ternary material layer is 3 wt%.

[0136] The boron-doped ternary material core and the boron-doped ternary material layer also include a gradient transition region with a thickness of 200 nm; in the gradient transition region, the boron content increases linearly from the direction closer to the boron-doped ternary material core to the direction closer to the boron-doped ternary material layer.

[0137] The boron-doped ternary material layer and the lithium fluoride coating layer also include a BOF bonding transition layer with a thickness of 200 nm.

[0138] The method for preparing the positive electrode precursor includes:

[0139] (1) Add nickel salt, cobalt salt and manganese salt to a solvent to obtain a mixed metal salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 96:2:2). Add the mixed metal salt solution, precipitant solution, complexing agent solution and boric acid solution in parallel to the reaction base liquid to form a reaction solution. Control the pH value of the reaction solution to 10.0, the ammonia concentration to 3g / L, the boron element concentration to 1800ppm and the temperature to 55℃. At the same time, stir at a speed of 550rpm. The first co-precipitation reaction is carried out in the reaction solution to obtain a solution containing a boron-doped ternary material core.

[0140] (2) Add nickel salt, cobalt salt and manganese salt to a solvent to obtain a mixed metal salt solution (the molar ratio of nickel ion, cobalt ion and manganese ion is 96:2:2). Add the mixed metal salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing boron-doped ternary material core obtained in step (1) to form a reaction solution. Control the pH value of the reaction solution to 11.0, the ammonia concentration to 5g / L, the boron element concentration to 3300ppm and the temperature to 55℃. Stir at 550rpm to carry out the second coprecipitation reaction in the reaction solution. After filtration, the obtained solid is washed with alkali and water in sequence, and then dried at 160℃ to obtain the precipitate.

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

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

[0143] Example 4

[0144] This embodiment provides a boron gradient-doped cathode precursor, wherein the mass fraction of boron in the boron-doped ternary material core is 0.02 wt%.

[0145] Except for the concentration of boron in the reaction solution of step (1) of the method for preparing the positive electrode precursor, which is 240 ppm, the rest of the steps are the same as in Example 1.

[0146] Example 5

[0147] This embodiment provides a boron gradient-doped cathode precursor, wherein the mass fraction of boron in the boron-doped ternary material core is 2 wt%.

[0148] Except for the concentration of boron in the reaction solution of step (1) of the method for preparing the positive electrode precursor, which is 3000 ppm, the rest of the steps are the same as in Example 1.

[0149] Example 6

[0150] This embodiment provides a boron gradient-doped positive electrode precursor, wherein the mass fraction of boron in the boron-doped ternary material layer is 1 wt%.

[0151] Except for the concentration of boron in the reaction solution of step (2) of the method for preparing the positive electrode precursor, which 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, wherein the mass fraction of boron in the boron-doped ternary material layer is 5 wt%.

[0154] Except for the concentration of boron in the reaction solution of step (2) of the method for preparing the positive electrode precursor, which is 4500 ppm, the rest of the steps are 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] The only difference between step (3) of the method for preparing the positive electrode precursor is that "the obtained mixed slurry is heated to 450°C at a heating rate of 6.5°C / min and kept at that temperature for 1.5h, and then heated to 550°C at a heating rate of 5°C / min and kept at that temperature for 2.5h to obtain the positive electrode precursor". The remaining steps are the same as in Example 1.

[0158] Comparative Example 1

[0159] This comparative example provides a boron gradient-doped cathode precursor, wherein the mass fraction of boron in the boron-doped ternary material core and the mass fraction of boron in the boron-doped ternary material layer are both 0.8 wt%, and there is no gradient transition region between the boron-doped ternary material core and the boron-doped ternary material layer.

[0160] Except for the concentration of boron in the reaction solution of step (2) of the method for preparing the positive electrode precursor, which 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 cathode precursor, wherein the mass fraction of boron in the boron-doped ternary material core and the mass fraction of boron in the boron-doped ternary material layer are both 2.2 wt%, and there is no gradient transition region between the boron-doped ternary material core and the boron-doped ternary material layer.

[0163] Except for the concentration of boron in the reaction solution of step (1) of the method for preparing the positive electrode precursor, which is 3000 ppm, the rest of the steps are the same as in Example 1.

[0164] Comparative Example 3

[0165] This comparative example provides a boron gradient-doped cathode precursor, wherein the mass fraction of boron in the boron-doped ternary material core is greater than the mass fraction of boron in the boron-doped ternary material layer, and in the gradient transition region, the boron content decreases linearly from the direction near the boron-doped ternary material core to the direction near the boron-doped ternary material layer.

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

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

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

[0169] Comparative Example 4

[0170] This comparative example provides a boron gradient-doped cathode precursor, except that the boron-doped ternary material core is replaced with an undoped ternary material core and the boron-doped ternary material layer is replaced with an undoped ternary material layer, and there is no gradient transition region between the boron-doped ternary material core and the boron-doped ternary material layer.

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

[0172] The positive electrode precursor provided in the above embodiments and comparative examples is mixed with lithium carbonate at a mass ratio of 1:1.05, and then sintered at 850°C for 12 hours to obtain the positive electrode material. The obtained positive electrode material is then mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 90:5:5, using N-methylpyrrolidone as the solvent, and stirred to form a slurry. The obtained slurry is then uniformly coated onto aluminum foil using a doctor blade with a coating gap of 100 μm. After coating, it is first dried by blowing air, then rolled and cut into circular electrode sheets, and then vacuum dried at 120°C. The weight of the electrode sheets is then weighed to obtain the positive electrode sheet of the button half-cell. The negative electrode is a lithium metal sheet, the separator is a PP microporous membrane, and the electrolyte is a basic lithium battery electrolyte. The positive electrode sheet, lithium metal sheet, separator, and electrolyte are assembled to obtain a button cell.

[0173] The electrochemical performance of the coin cells was tested at 25℃, within a voltage range of 2.8 to 4.3V, and at a rate of 5C. The first discharge specific capacity of the coin cells is shown in Table 1.

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

[0175] The electrochemical performance of the coin cells was tested at 25°C, within a voltage range of 2.8–4.3V, and at a rate of 1C. The capacity retention rate after 500 cycles is shown in Table 1.

[0176] A fully charged battery (e.g., 100% SOC) is placed in an insulated, sealed cavity with an initial temperature of 50°C. The temperature is increased in 0.5°C increments. When the self-heating temperature rise rate is detected to be ≥0.02°C / min, the adiabatic tracking mode is triggered to record temperature and pressure changes in real time, thereby obtaining the thermal runaway initiation temperature as shown in Table 1. The thermal runaway initiation temperature is defined as the inflection point of irreversible acceleration of self-heating (corresponding to a temperature rise rate ≥1°C / min).

[0177] Table 1

[0178]

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

[0180] (1) A battery containing a cathode material prepared from the boron gradient doped cathode precursor provided in Examples 1 to 3 exhibits a higher discharge specific capacity and a higher capacity retention.

[0181] (2) By comparing Example 1 with Examples 4 and 5, it can be seen that in this invention, taking the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of boron in the boron-doped ternary material core affects the performance of the cathode precursor, cathode material and battery. When the mass fraction of boron in the boron-doped ternary material core is 0.1 to 1.5 wt%, the cathode precursor and cathode material have better performance. This is because when the mass fraction of boron in the boron-doped ternary material core is 0.1 to 1.5 wt%, a strong BO bond is formed by embedding an appropriate amount of boron into the lattice, which enhances the rigidity of the core crystal structure, inhibits cation mixing and high-temperature oxygen loss, and avoids lithium-ion diffusion obstruction caused by excessive doping, thus maintaining lattice integrity. The low boron concentration in the core and the high boron concentration in the outer layer are connected through a gradient transition region, so that the boron content changes linearly, reducing stress concentration caused by lattice abrupt changes and synergistically suppressing the propagation of bulk cracks.

[0182] (3) By comparing Example 1 with Examples 6 and 7, it can be seen that in this invention, the mass fraction of the boron-doped ternary material layer is taken as 100%. The mass fraction of boron in the boron-doped ternary material layer will affect the performance of the cathode precursor and cathode material. When the mass fraction of boron in the boron-doped ternary material layer is 1.5 to 3 wt%, the cathode precursor and cathode material have better performance. This is because this range of boron content can both enhance the synergistic effect between the boron-doped ternary material layer and the lithium fluoride coating layer to form a stable BOF bonded transition layer to inhibit electrolyte erosion and transition metal dissolution, and avoid the blockage of lithium ion transport channels caused by excessive boron enrichment, thus balancing the structural stability and electrochemical kinetic performance of the material.

[0183] (4) By comparing Example 1 and Example 8, it can be seen that in the present invention, lithium fluoride in the lithium fluoride coating layer reacts with 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 effect, which not only alleviates the lattice stress caused by volume change during charging and discharging, but also suppresses oxygen release and phase change exothermic at high temperature through the strong covalentity of BOF bonds, thus synergistically enhancing the structural stability and thermal stability of the cathode precursor.

[0184] (5) As can be seen from the comparison between Example 1 and Comparative Examples 1 to 4, in the positive electrode precursor provided by the present invention, both the boron-doped ternary material core and the boron-doped ternary material layer are boron-doped. Since boron has a small ionic radius, it is embedded in the lattice to form BO bonds with high bond energy, which effectively enhances the rigidity of the crystal structure and suppresses oxygen loss and phase transition at high temperature, thereby enhancing the structural stability and thermal stability of the positive electrode precursor and the positive electrode material prepared from 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 from the positive electrode precursor.

[0185] In the cathode precursor provided by this invention, the mass fraction of boron in the boron-doped ternary material core is lower than that in the boron-doped ternary material layer. The boron-doped ternary material core has a lower boron concentration, which maintains the lattice integrity of the boron-doped ternary material core while avoiding lithium diffusion obstruction caused by excessive doping, thus ensuring that the cathode material prepared from the cathode precursor has good electrochemical performance. The boron-doped ternary material layer has a higher boron concentration, which improves the structural and thermal stability of the boron-doped ternary material layer, strengthens the surface and interface structure of the cathode precursor, and inhibits crack propagation from the surface of the cathode precursor to the interior, thereby improving the structural stability of the cathode 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 conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection 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 covering the outside of the boron-doped ternary material core; The mass fraction of boron in the boron-doped ternary material core is lower than the mass fraction of boron in the boron-doped ternary material layer. The chemical formula of the positive electrode precursor is Ni. x Co y Mn z B w (OH)2, where 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; Taking the mass fraction of the boron-doped ternary material core as 100%, the mass fraction of boron in the boron-doped ternary material core is 0.1~1.5wt%, and the mass fraction of boron in the boron-doped ternary material layer is 1.5~3wt%. The boron-doped ternary material core and the boron-doped ternary material layer also include a gradient transition region.

2. The positive electrode precursor according to claim 1, characterized in that, In the gradient transition region, the boron content increases linearly from the direction near the boron-doped ternary material core to the direction near the boron-doped ternary material layer.

3. The positive electrode precursor according to claim 1, characterized in that, The thickness of the gradient transition region is 200~500nm.

4. The positive electrode precursor according to claim 1, characterized in that, The positive electrode precursor also includes a lithium fluoride coating layer covering the outside of the boron-doped ternary material layer.

5. The positive electrode precursor according to claim 4, characterized in that, The boron-doped ternary material layer and the lithium fluoride coating layer also include a BOF bonding transition layer.

6. The positive electrode precursor according to claim 5, characterized in that, The thickness of the BOF bonding transition layer is 200~800nm.

7. A method for preparing the positive electrode precursor according to any one of claims 1 to 6, characterized in that, The preparation method includes: (1) A metal mixed salt solution, a precipitant solution, a complexing agent solution and a boron source are added to the reaction base liquid in parallel to form a reaction solution. The first co-precipitation reaction occurs in the reaction solution to obtain a solution containing a boron-doped ternary material core. (2) The metal mixed salt solution, precipitant solution, complexing agent solution and boron source are added in parallel to the solution containing the boron-doped ternary material core obtained in step (1) to form a reaction solution. The second coprecipitation reaction is carried out in the reaction solution to obtain the positive electrode precursor. The concentration of the boron source in the reaction solution in step (1) is less than the concentration of the boron source in the reaction solution in step (2).

8. The preparation method according to claim 7, characterized in that, In step (1), the pH of the reaction solution is controlled to be 9.0~10.0 in the first coprecipitation reaction.

9. The preparation method according to claim 7, characterized in that, In step (1), the concentration of ammonia in the reaction solution is controlled to be 2-3 g / L in the first coprecipitation reaction.

10. The preparation method according to claim 7, characterized in that, In step (1), the concentration of boron in the reaction solution is controlled to be 1200~1800 ppm.

11. The preparation method according to claim 7, characterized in that, The time ratio of the first coprecipitation reaction in step (1) to the second coprecipitation reaction in step (2) is 1:(1~2).

12. The preparation method according to claim 7, characterized in that, In step (2), the pH of the reaction solution is controlled to be 11.0~12.0 in the second coprecipitation reaction.

13. The preparation method according to claim 7, characterized in that, In step (2), the concentration of ammonia in the reaction solution is controlled to be 5~7 g / L.

14. The preparation method according to claim 7, characterized in that, In step (2), the concentration of boron in the reaction solution is controlled to be 2700~3300 ppm.

15. The preparation method according to claim 7, characterized in that, The preparation method further includes step (2) after the second coprecipitation reaction: The precipitate obtained from the second coprecipitation reaction, lithium fluoride, and solvent are mixed to obtain a mixed slurry. The resulting mixed slurry is then heat-treated to obtain a positive electrode precursor.

16. The preparation method according to claim 15, characterized in that, The mass ratio of the precipitate obtained from the second coprecipitation reaction in the mixture to lithium fluoride is 1:(0.01~0.02).

17. The preparation method according to claim 15, characterized in that, The solid content of the mixed slurry is 20-30%.

18. The preparation method according to claim 15, characterized in that, The heat treatment includes a first heating, a first holding, a second heating, and a second holding, performed sequentially.

19. The preparation method according to claim 18, characterized in that, The heating rate of the first heating is 5~8℃ / min, and the final temperature is 400~500℃.

20. The preparation method according to claim 18, characterized in that, The first heat preservation time is 1~2 hours.

21. The preparation method according to claim 18, characterized in that, The second heating rate is 4~6℃ / min, and the final temperature is 500~600℃.

22. The preparation method according to claim 18, characterized in that, The first heat preservation time is 2-3 hours.

23. The preparation method according to claim 7, characterized in that, The preparation method includes: (1) Add nickel salt, cobalt salt and manganese salt to a solvent to obtain a mixed metal salt solution. Add the mixed metal salt solution, precipitant solution, complexing agent solution and boric acid solution in parallel to the reaction base liquid to form a reaction solution. Control the pH value of the reaction solution to 9.0~10.0, the ammonia concentration to 2-3 g / L, the boron element concentration to 1200~1800 ppm and the temperature to 55~65℃. Stir at a speed of 550~650 rpm. A first co-precipitation reaction is carried out in the reaction solution to obtain a solution containing a boron-doped ternary material core. (2) Add nickel salt, cobalt salt and manganese salt to a solvent to obtain a mixed metal salt solution. Add the mixed metal salt solution, precipitant solution, complexing agent solution and boron source in parallel to the solution containing boron-doped ternary material core obtained in step (1) to form a reaction solution. Control the pH value of the reaction solution to 11.0~12.0, the ammonia concentration to 5~7g / L, the boron element concentration to 2700~3300ppm and the temperature to 55~65℃. Stir at a speed of 550~650rpm to carry out the second coprecipitation reaction in the reaction solution. After filtration, the obtained solid is washed with alkali and water in sequence, and then dried at 80~160℃ to obtain the precipitate. The time ratio of the first coprecipitation reaction in step (1) to the second coprecipitation reaction in step (2) is 1:(1~2); (3) The precipitate obtained in step (2) is mixed with lithium fluoride and solvent by heating and stirring at 60~80℃ to obtain a mixed slurry with a solid content of 20~30%. The mass ratio of the precipitate obtained in step (2) to lithium fluoride in the mixed slurry is 1:(0.01~0.02). The mixed slurry is then heated to 400~500℃ at a heating rate of 5~8℃ / min and kept at that temperature for 1~2h. Then, it is heated to 500~600℃ at a heating rate of 4~6℃ / min and kept at that temperature for 2~3h to obtain the positive electrode precursor.

24. A positive electrode material, characterized in that, The cathode material is prepared from the cathode precursor according to any one of claims 1 to 6.

25. A battery, characterized in that, The battery comprises the positive electrode material as described in claim 24.

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