Precursor and positive electrode material sequentially loosened in radial direction, and preparation and application of precursor and positive electrode material

Abstract

The invention provides a precursor sequentially loosened in the radial direction, a positive electrode material and preparation and application of the precursor and the positive electrode material. The precursor comprises a seed crystal and a shell layer wrapping the outside of the seed crystal. The density of the shell layer is lower than that of the seed crystal, and in the radial direction of the precursor, the density of the shell layer is sequentially reduced in the direction from the position close to the seed crystal to the position away from the seed crystal. According to the present invention, the seed crystal density of the precursor sequentially loosened along the radial direction is high, and the density of the shell layer is low so as to form the structure with the compact inner part and sequentially looser from inside to outside, such that the internal resistance of the positive electrode material prepared from the precursor is reduced, and the lithium ion transmission path of the positive electrode material is shortened; therefore, the battery comprising the positive electrode material prepared from the precursor shows excellent electrochemical performance.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and relates to a precursor which is loosened in sequence along a radial direction, and in particular to a precursor which is loosened in sequence along a radial direction, a positive electrode material, and preparation and application thereof. Background Art

[0002] As people's living needs grow, the performance requirements for battery materials are getting higher and higher. Lithium-ion batteries play an important role in new energy vehicles, electronic products and energy storage due to their advantages such as high energy density, low cost and long cycle life. High-nickel layered cathode materials are considered to be one of the ideal cathode materials in power batteries due to their high specific capacity, high discharge voltage, low toxicity and low cost. However, they still have problems with capacity decay and poor thermal stability during the cycle.

[0003] CN112142123A discloses a network structure precursor and a composite oxide powder, and a preparation method and application thereof. The network structure precursor comprises a loose inner core and a loose outer shell layer coated on the surface of the loose inner core, wherein the main component of the loose inner core is a divalent nickel-cobalt-manganese composite hydroxide, and the main component of the loose outer shell layer is a trivalent nickel-cobalt-manganese composite hydroxide, and the particle size of the nickel-cobalt-manganese network structure precursor is 2 to 30 μm. The lithium-ion battery corresponding to the network structure precursor provided in the document has an initial charge and discharge efficiency of ≥95% at 0.2C and an initial charge and discharge efficiency of ≥92% at 10C under low temperature (-10°C), which can improve low temperature power performance and has great industrial application prospects.

[0004] CN108615868A discloses a nickel-cobalt-manganese ternary material precursor with high sphericity, dense surface and low impurities, as well as its preparation method and application, which belongs to the technical field of lithium-ion battery preparation. The preparation method of the document includes the following steps: dissolving nickel source, cobalt source and manganese source compounds in deionized water to prepare a solution of a certain concentration; then mixing the prepared solution with concentrated ammonia water, and then flowing it into a reactor with a precipitant and an ammonium salt solution to react; then washing the obtained precursor slurry with water, re-slurrying, and then washing it with water again, and adding a certain amount of alkaline solution during the re-slurrying process; finally spray drying, and the nickel-cobalt-manganese ternary material precursor of the document can be obtained.

[0005] The precursors of the positive electrode materials disclosed in the prior art all have certain defects. The positive electrode materials prepared from the precursors have a short lithium ion transmission path and a large internal resistance, which leads to poor electrochemical performance of the battery of the positive electrode materials. Therefore, it is very important to develop and design a new type of precursor, positive electrode material and its preparation. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a precursor, a positive electrode material and their preparation and application which are loosened in sequence along the radial direction. The precursor provided by the present invention which is loosened in sequence along the radial direction has a higher seed density and a lower shell density, thereby forming a structure which is compact inside and becomes looser from the inside to the outside, thereby reducing the internal resistance of the positive electrode material prepared from the precursor and shortening the lithium ion transmission path of the positive electrode material; therefore, a battery containing the positive electrode material prepared from the precursor exhibits excellent electrochemical properties.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a precursor which is loosened in radial order, the precursor comprising a seed crystal and a shell layer covering the seed crystal;

[0009] The density of the shell layer is lower than the density of the seed crystal, and in the radial direction of the precursor, the density of the shell layer decreases in sequence from the direction close to the seed crystal to the direction away from the seed crystal.

[0010] The precursor provided by the present invention has a high density of seeds and a low density of shells, thereby forming a structure that is compact inside and becomes looser from the inside to the outside, thereby reducing the internal resistance of the positive electrode material prepared from the precursor and shortening the lithium ion transmission path of the positive electrode material; therefore, the battery containing the positive electrode material prepared from the precursor exhibits excellent electrochemical properties.

[0011] Preferably, along the direction from close to the seed crystal to far away from the seed crystal, the shell layer includes a first shell layer, a second shell layer and a third shell layer which are sequentially coated and have successively decreasing densities.

[0012] In a second aspect, the present invention provides a method for preparing the precursor according to the first aspect, the preparation method comprising:

[0013] (1) adding a mixed metal salt solution, a precipitant solution and a complexing agent solution to a reaction base solution in parallel, adjusting the reaction conditions, and performing a coprecipitation reaction to obtain seed crystals and a first slurry, and then adding the obtained seed crystals to the first slurry to obtain a second slurry;

[0014] (2) adding the mixed metal salt solution, the precipitant solution and the complexing agent solution to the second slurry obtained in step (1) in stages and in parallel, adjusting the reaction conditions, and performing a coprecipitation reaction to obtain the precursor;

[0015] The staged addition comprises at least two stages, wherein the addition rate of the mixed metal salt solution in the first stage of the staged addition is not lower than the addition rate of the mixed metal salt solution in step (1), and the addition rate of the mixed metal salt solution in each previous stage is lower than the addition rate of the mixed metal salt solution in the adjacent next stage.

[0016] Preferably, the addition rate of the mixed metal salt solution in step (1) is 10 to 80 L / h, for example, 10 L / h, 20 L / h, 30 L / h, 40 L / h, 50 L / h, 60 L / h, 70 L / h or 80 L / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] Preferably, the mixed metal salt solution in step (1) and step (2) includes nickel ions, cobalt ions and manganese ions.

[0018] Preferably, the method for preparing the mixed metal salt solution in step (1) and step (2) comprises mixing water, a nickel source, a cobalt source and a manganese source, wherein the nickel source, the cobalt source and the manganese source are preferably sulfates.

[0019] Preferably, the total concentration of metal ions in the mixed metal salt solution in step (1) and step (2) is 1-2.5 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is (90-96):(2-6):(2-4).

[0020] The molar ratio of nickel ions to cobalt ions in the mixed metal salt solution in step (1) and step (2) of the present invention is (90-96):(2-6), for example, it can be 90:2, 90:4, 90:5, 90:6, 91:2, 91:3, 91:4, 91:5, 91:6, 93:2, 93:4, 93:5, 95:2, 95:3, 95:4, 95:6, 96:2, 96:4 or 96:5, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] The ratio of (90-96):(2-4) in the mixed metal salt solution in step (1) and step (2) of the present invention may be, for example, 90:2, 90:4, 91:2, 91:3, 91:4, 93:2, 93:4, 95:2, 95:3, 95:4, 96:2 or 96:4, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the total concentration of metal ions in the mixed metal salt solution in step (1) and step (2) is 1 to 2.5 mol / L, for example, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L or 2.5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the addition rate of the precipitant solution in step (1) is 2 to 20 L / h, for example, 2 L / h, 4 L / h, 6 L / h, 8 L / h, 10 L / h, 12 L / h, 14 L / h, 16 L / h, 18 L / h or 20 L / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the precipitant solution in step (1) and step (2) comprises any one of sodium hydroxide solution, potassium hydroxide solution or calcium hydroxide solution, or a combination of at least two of them. Typical but non-limiting combinations include a combination of sodium hydroxide solution and potassium hydroxide solution, a combination of potassium hydroxide solution and calcium hydroxide solution, or a combination of sodium hydroxide solution, potassium hydroxide solution and calcium hydroxide solution.

[0025] Preferably, the mass concentration of the precipitant solution in step (1) and step (2) is 30-35wt%, for example, 30wt%, 30.5wt%, 31wt%, 31.5wt%, 32wt%, 32.5wt%, 33wt%, 33.5wt%, 34wt%, 34.5wt% or 35wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the addition rate of the complexing agent solution in step (1) is 2 to 20 L / h, for example, it can be 2 L / h, 4 L / h, 6 L / h, 8 L / h, 10 L / h, 12 L / h, 14 L / h, 16 L / h, 18 L / h or 20 L / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the complexing agent solution in step (1) and step (2) comprises aqueous ammonia.

[0028] Preferably, the concentration of the complexing agent solution in step (1) and step (2) is 10-20wt%, for example, 10wt%, 12wt%, 14wt%, 16wt%, 18wt% or 20wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, the pH of the reaction base solution in step (1) is 11-12, the ammonia concentration is 4-10 g / L, and the temperature is 40-80°C.

[0030] The pH of the reaction base solution in step (1) of the present invention is 11-12, for example, 11, 11.2, 11.4, 11.6, 11.8 or 12, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] The ammonia concentration of the reaction base solution in step (1) of the present invention is 4 to 10 g / L, for example, 4 g / L, 4.5 g / L, 5 g / L, 5.5 g / L, 6 g / L, 6.5 g / L, 7 g / L, 7.5 g / L, 8 g / L, 8.5 g / L, 9 g / L, 9.5 g / L or 10 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] The temperature of the reaction base solution in step (1) of the present invention is 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, the method for preparing the reaction base solution comprises: mixing water, a precipitant and a complexing agent solution in a protective atmosphere.

[0034] Preferably, the adjusting reaction conditions in step (1) includes adjusting the pH to 11-11.5, the ammonia concentration to 5-6 g / L, and the stirring speed to 200-400 rpm.

[0035] The step (1) of adjusting the reaction conditions of the present invention includes adjusting the pH to 11 to 11.5, for example, 11, 11.1, 11.2, 11.3, 11.4 or 11.5, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0036] The adjusting reaction conditions in step (1) of the present invention include adjusting the ammonia concentration to 5-6 g / L, for example, 5 g / L, 5.1 g / L, 5.2 g / L, 5.3 g / L, 5.4 g / L, 5.5 g / L, 5.6 g / L, 5.7 g / L, 5.8 g / L, 5.9 g / L or 6 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the adjusting the reaction conditions in step (1) includes adjusting the temperature to 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Preferably, the D50 particle size of the seed crystal in step (1) is 2 to 5 μm, for example, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, step (1) further comprises solid-liquid separation, washing and drying performed sequentially between the coprecipitation reaction and the addition of the seed crystals to the first slurry.

[0040] Preferably, when the seed crystals obtained in step (1) are added to the first slurry, water and the complexing agent solution are added simultaneously.

[0041] Preferably, the solid content of the seed crystals in the second slurry obtained in step (1) is 20-60 g / L, the ammonia concentration is 4-6 g / L, and the temperature is 50-70°C.

[0042] The solid content of the seed crystals in the second slurry obtained in step (1) of the present invention is 20 to 60 g / L, for example, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L or 50 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] The ammonia concentration in the second slurry obtained in step (1) of the present invention is 4 to 6 g / L, for example, 4 g / L, 4.2 g / L, 4.4 g / L, 4.6 g / L, 4.8 g / L, 5 g / L, 5.2 g / L, 5.4 g / L, 5.6 g / L or 5.8 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] The temperature of the second slurry obtained in step (1) of the present invention is 50-70°C, for example, 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C or 70°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the staged process of step (2) comprises three stages, wherein the addition rate of the mixed metal salt solution increases successively, the pH value decreases successively, the ammonia concentration decreases successively, and the stirring speed decreases successively in the first stage, the second stage and the third stage.

[0046] Preferably, in the first stage, the mixed metal salt solution, the precipitant solution and the complexing agent solution are added in parallel to the second slurry obtained in step (1), the reaction conditions are adjusted, and a co-precipitation reaction is carried out to obtain a primary mixed solution containing a first precipitate.

[0047] Preferably, the rate of addition of the mixed metal salt solution in the first stage is the same as the rate of addition of the mixed metal salt solution in step (1).

[0048] Preferably, the adjusting reaction conditions in the first stage include adjusting the pH to 10.5-11.0, the ammonia concentration to 4-5 g / L, and the stirring speed to 200-350 rpm.

[0049] The adjusting reaction conditions in the first stage of the present invention include adjusting the pH to 10.5-11.0, for example, 10.5, 10.6, 10.7, 10.8, 10.9 or 11, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] The adjusting reaction conditions in the first stage of the present invention include adjusting the ammonia concentration to 4-5 g / L, for example, it can be 4g / L, 4.1g / L, 4.2g / L, 4.3g / L, 4.4g / L, 4.5g / L, 4.6g / L, 4.7g / L, 4.8g / L, 4.9g / L or 5g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] The adjusting reaction conditions in the first stage of the present invention include adjusting the stirring speed to 200-350 rpm, for example, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm or 350 rpm, but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] Preferably, the adjusting reaction conditions in the first stage also includes adjusting the temperature to 50-70°C, for example, it can be 50-70°C, for example, it can be 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] Preferably, the first stage further comprises continuously adding a surfactant to the second slurry.

[0054] In the present invention, a surfactant is added in the first stage, and the surfactant can prevent the primary particles formed during coprecipitation from sticking together, and can make the primary particles grow in the direction of slender strips, thereby increasing the pores between the primary particles, which is conducive to forming a loose and porous structure, thereby shortening the transmission path of lithium ions in the positive electrode material prepared from the precursor and reducing the internal resistance.

[0055] Preferably, the surfactant comprises sodium lauryl sulfate.

[0056] Preferably, the concentration of the surfactant during the coprecipitation reaction in the first stage is maintained at 0.02-0.1 mol / L, for example, it can be 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L or 0.1 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0057] Preferably, the D50 particle size of the first precipitate obtained in the first stage is 5 to 7 μm, for example, it can be 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm or 7 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0058] Preferably, in the second stage, the mixed metal salt solution, the precipitant solution and the complexing agent solution are added to the obtained primary mixed solution in parallel, the reaction conditions are adjusted, a co-precipitation reaction is carried out, and a remixed solution containing a second precipitate is obtained.

[0059] Preferably, the addition rate of the mixed metal salt solution in the second stage is 25 to 35 L / h, for example, it can be 25 L / h, 26 L / h, 27 L / h, 28 L / h, 29 L / h, 30 L / h, 31 L / h, 32 L / h, 33 L / h, 34 L / h or 35 L / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0060] Preferably, the adjusting reaction conditions in the second stage include adjusting the pH to 10.3-10.8, the ammonia concentration to 3.5-4.5 g / L, and the stirring speed to 180-300 rpm.

[0061] The adjusting reaction conditions in the second stage of the present invention include adjusting the pH to 10.3-10.8, for example, 10.3, 10.35, 10.4, 10.45, 10.5, 10.55, 10.6, 10.65, 10.7, 10.75 or 10.8, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] The adjusting reaction conditions in the second stage of the present invention include adjusting the ammonia concentration to 3.5-4.5 g / L, for example, 3.5 g / L, 3.6 g / L, 3.7 g / L, 3.8 g / L, 3.9 g / L, 4 g / L, 4.1 g / L, 4.2 g / L, 4.3 g / L, 4.4 g / L or 4.5 g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0063] The adjusting reaction conditions in the second stage of the present invention include adjusting the stirring speed to 180-300 rpm, for example, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm or 300 rpm, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0064] Preferably, the adjusting reaction conditions in the second stage also includes adjusting the temperature to 50-70°C, for example, it can be 50-70°C, for example, it can be 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0065] Preferably, the second stage further comprises continuously adding a surfactant to the initial mixed liquid.

[0066] In the present invention, a surfactant is added in the second stage, and the surfactant can prevent the primary particles formed during coprecipitation from sticking together, and can make the primary particles grow in the direction of slender strips, thereby increasing the pores between the primary particles, which is conducive to forming a loose and porous structure, thereby shortening the transmission path of lithium ions in the positive electrode material prepared from the precursor and reducing the internal resistance.

[0067] Preferably, the concentration of the surfactant during the coprecipitation reaction in the second stage is maintained at 0.02-0.1 mol / L, for example, it can be 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L or 0.1 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0068] Preferably, the D50 particle size of the second precipitate obtained in the second stage is 7 to 9 μm, for example, it can be 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8 μm, 8.2 μm, 8.4 μm, 8.6 μm, 8.8 μm or 9 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0069] Preferably, in the third stage, the mixed metal salt solution, the precipitant solution and the complexing agent solution are added in parallel to the obtained remixed solution, the reaction conditions are adjusted, and a coprecipitation reaction is performed to obtain a final mixed solution containing the precursor.

[0070] Preferably, the addition rate of the mixed metal salt solution in the third stage is 35 to 45 L / h, for example, it can be 35 L / h, 36 L / h, 37 L / h, 38 L / h, 39 L / h, 40 L / h, 41 L / h, 42 L / h, 43 L / h, 44 L / h or 45 L / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0071] Preferably, the adjusting reaction conditions in the third stage include adjusting the pH to 10.0-10.5, the ammonia concentration to 3-4 g / L, and the stirring speed to 150-250 rpm.

[0072] The adjusting reaction conditions in the third stage of the present invention include adjusting the pH to 10.0-10.5, for example, 10.0, 10.05, 10.1, 10.15, 10.2, 10.25, 10.3, 10.35, 10.4, 10.45 or 10.5, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0073] The adjusting reaction conditions in the third stage of the present invention include adjusting the ammonia concentration to 3-4 g / L, for example, 3 g / L, 3.1 g / L, 3.2 g / L, 3.3 g / L, 3.4 g / L, 3.5 g / L, 3.6 g / L, 3.7 g / L, 3.8 g / L, 3.9 g / L or 4 g / L, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0074] The adjusting reaction conditions in the third stage of the present invention include adjusting the stirring speed to 150-250 rpm, for example, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm or 250 rpm, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0075] Preferably, the adjusting reaction conditions in the third stage also includes adjusting the temperature to 50-70°C, for example, it can be 50-70°C, for example, it can be 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0076] Preferably, the third stage further comprises continuously adding a surfactant to the initial mixed liquid.

[0077] In the present invention, a surfactant is added in the third stage, which can prevent the primary particles formed during coprecipitation from sticking together, and can make the primary particles grow in the direction of slender strips, thereby increasing the pores between the primary particles and facilitating the formation of a loose and porous structure, thereby shortening the transmission path of lithium ions in the positive electrode material prepared from the precursor and reducing the internal resistance.

[0078] Preferably, the concentration of the surfactant during the coprecipitation reaction in the third stage is maintained at 0.02-0.1 mol / L, for example, it can be 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L or 0.1 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0079] Preferably, the D50 particle size of the precursor obtained in the third stage is 9 to 15 μm, for example, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0080] In a third aspect, the present invention provides a boron-coated positive electrode material, wherein the positive electrode material is prepared from the precursor described in the first aspect.

[0081] The improvement of positive electrode materials usually uses two methods: element doping and surface coating. The coating technology is used to generate a coating layer on the surface of the positive electrode material, which can isolate the positive electrode material and the electrolyte to avoid interface side reactions.

[0082] The positive electrode material of the present invention has a boron coating layer, which prevents the electrolyte from corroding the positive electrode material, thereby improving the rate performance and stability of the battery containing the positive electrode material.

[0083] Preferably, the mass fraction of the boron element in the positive electrode material is 0.005-0.02wt%, for example, it can be 0.005wt%, 0.007wt%, 0.009wt%, 0.01wt%, 0.012wt%, 0.014wt%, 0.016wt%, 0.018wt% or 0.02wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0084] In a fourth aspect, the present invention provides a process for preparing the positive electrode material according to the third aspect, the preparation process comprising:

[0085] The precursor is mixed with a lithium source and then sintered once to obtain a sintered product. The sintered product is mixed with a boron source and then sintered twice to obtain a boron-coated positive electrode material.

[0086] Preferably, the mass ratio of the precursor to the lithium source is 1:(1-1.2), for example, it can be 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.1, 1:1.12, 1:1.14, 1:1.16, 1:1.18 or 1:1.2, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0087] Preferably, the primary sintering is carried out at a temperature of 500 to 800° C. and for a time of 6 to 10 hours.

[0088] The primary sintering temperature in the present invention is 500-800°C, for example, it can be 500°C, 520°C, 550°C, 570°C, 600°C, 620°C, 650°C, 670°C, 700°C, 720°C, 750°C, 770°C or 800°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0089] The primary sintering time in the present invention is 6 to 10 hours, for example, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours or 10 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0090] Preferably, the secondary sintering is carried out at a temperature of 200 to 500° C. and for a time of 2 to 6 hours.

[0091] The temperature of the secondary sintering in the present invention is 200-500°C, for example, it can be 200°C, 230°C, 250°C, 270°C, 300°C, 320°C, 350°C, 370°C, 400°C, 420°C, 450°C, 470°C or 500°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0092] Preferably, the lithium source comprises lithium hydroxide and / or lithium carbonate.

[0093] Preferably, the boron source comprises boric acid.

[0094] In a fifth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode material described in the third aspect.

[0095] Compared with the prior art, the present invention has the following beneficial effects:

[0096] (1) The precursor provided by the present invention has a high seed density and a low shell density, thereby forming a structure that is compact inside and looser from the inside to the outside, thereby reducing the internal resistance of the positive electrode material prepared from the precursor and shortening the lithium ion transmission path of the positive electrode material; therefore, the battery containing the positive electrode material prepared from the precursor exhibits excellent electrochemical performance;

[0097] (2) In the present invention, by adding a surfactant in the first stage, the second stage and the third stage, the surfactant can prevent the primary particles formed during coprecipitation from sticking together, and can make the primary particles grow in the direction of slender strips, thereby increasing the pores between the primary particles, which is conducive to forming a loose and porous structure, thereby shortening the transmission path of lithium ions in the positive electrode material prepared from the precursor and reducing the internal resistance;

[0098] (3) The positive electrode material of the present invention has a boron coating layer, which prevents the electrolyte from corroding the positive electrode material, thereby improving the rate performance and stability of the battery containing the positive electrode material. DETAILED DESCRIPTION

[0099] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0100] Example 1

[0101] This embodiment provides a precursor that is loosened in radial direction, the precursor comprising a seed crystal, and a shell layer coated outside the seed crystal with a density lower than that of the seed crystal;

[0102] In the radial direction of the precursor, along the direction from close to the seed crystal to far away from the seed crystal, the shell layer includes a first shell layer, a second shell layer and a third shell layer which are sequentially covered and have successively smaller densities.

[0103] The preparation method of the precursor is:

[0104] (1) adding a mixed metal salt solution (the total concentration of metal ions is 1.5 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 93:4:3), sodium hydroxide solution and ammonia water to the reaction bottom liquid in parallel, adjusting the pH to 11.2-11.4, the ammonia concentration to 5.5 g / L, the stirring speed to 300 rpm, and the temperature to 50° C., to carry out a coprecipitation reaction, and sequentially carry out solid-liquid separation, washing and drying to obtain a seed crystal with a D50 particle size of 3.5 μm and a first slurry, and then adding the obtained seed crystal, water and ammonia water to the first slurry in parallel to obtain a second slurry with a solid content of 40 g / L of the seed crystal, an ammonia concentration of 5 g / L and a temperature of 60° C.;

[0105] The addition rate of the mixed metal salt solution was 25 L / h, the pH of the reaction bottom solution was 11.5, the ammonia concentration was 7 g / L, and the temperature was 60°C;

[0106] (2) adding a mixed metal salt solution (the total concentration of metal ions is 1.5 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 93:4:3), a sodium hydroxide solution and ammonia water in three stages to the second slurry obtained in step (1), adjusting the reaction conditions, and performing a coprecipitation reaction to obtain the precursor;

[0107] The first stage: adding a mixed metal salt solution, a sodium hydroxide solution and an ammonia solution to the second slurry obtained in step (1) in parallel, and continuously adding a surfactant, the adding speed of the mixed metal salt solution is the same as the adding speed of the mixed metal salt solution in step (1), adjusting the pH to 10.6-10.9, the ammonia concentration to 4.5 g / L, the stirring speed to 270 rpm, the concentration of the surfactant to be maintained at 0.06 mol / L, and performing a coprecipitation reaction to obtain a primary mixed solution containing a first precipitate with a D50 particle size of 6 μm;

[0108] The second stage: adding the mixed metal salt solution, sodium hydroxide solution and ammonia water to the obtained primary mixed solution in parallel, and continuously adding the surfactant, the adding rate of the mixed metal salt solution is 30 L / h, the pH is adjusted to 10.2-10.6, the ammonia concentration is 4 g / L, the stirring speed is 240 rpm, the concentration of the surfactant is maintained at 0.06 mol / L, and a coprecipitation reaction is carried out to obtain a remixed solution containing a second precipitate with a D50 particle size of 8 μm;

[0109] The third stage: adding the mixed metal salt solution, sodium hydroxide solution and ammonia water to the obtained remixed liquid in parallel, and continuously adding the surfactant, the addition rate of the mixed metal salt solution is 40L / h, the pH is adjusted to 10.1-10.4, the ammonia concentration is 3.5g / L, the stirring speed is 200rpm, the concentration of the surfactant is maintained at 0.06mol / L, and a coprecipitation reaction is carried out to obtain a final mixed solution containing a precursor with a D50 particle size of 12μm.

[0110] This embodiment also provides a boron-coated positive electrode material, in which the mass fraction of boron element in the positive electrode material is 0.01wt%, and the preparation process of the boron-coated positive electrode material is as follows:

[0111] The precursor having a mass ratio of 1:1.1 is mixed with a lithium source and sintered at 650° C. for 8 hours to obtain a sintered product; the sintered product is mixed with boric acid and sintered at 350° C. for 4 hours to obtain a boron-coated positive electrode material.

[0112] Example 2

[0113] This embodiment provides a precursor that is loosened in radial direction, the precursor comprising a seed crystal, and a shell layer coated outside the seed crystal with a density lower than that of the seed crystal;

[0114] In the radial direction of the precursor, along the direction from close to the seed crystal to far away from the seed crystal, the shell layer includes a first shell layer, a second shell layer and a third shell layer which are sequentially covered and have successively smaller densities.

[0115] The preparation method of the precursor is:

[0116] (1) adding a mixed metal salt solution (the total concentration of metal ions is 1 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 90:6:4), sodium hydroxide solution and ammonia water to the reaction bottom liquid in parallel, adjusting the pH to 11.0-11.2, the ammonia concentration to 5 g / L, the stirring speed to 200 rpm, and the temperature to 60° C., to carry out a coprecipitation reaction, and sequentially carry out solid-liquid separation, washing and drying to obtain a seed crystal with a D50 particle size of 2 μm and a first slurry, and then adding the obtained seed crystal, water and ammonia water to the first slurry in parallel to obtain a second slurry with a seed crystal solid content of 20 g / L, an ammonia concentration of 4 g / L and a temperature of 70° C.;

[0117] The addition rate of the mixed metal salt solution was 30 L / h, the pH of the reaction bottom solution was 11, the ammonia concentration was 4 g / L, and the temperature was 80°C;

[0118] (2) adding a mixed metal salt solution (the total concentration of metal ions is 1 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 90:6:4), a sodium hydroxide solution and ammonia water in three stages to the second slurry obtained in step (2), adjusting the reaction conditions, and performing a coprecipitation reaction to obtain the precursor;

[0119] The first stage: adding a mixed metal salt solution, a sodium hydroxide solution and an ammonia solution to the second slurry obtained in step (1) in parallel, and continuously adding a surfactant, the adding speed of the mixed metal salt solution is the same as the adding speed of the mixed metal salt solution in step (1), adjusting the pH to 10.5-10.7, the ammonia concentration to 4 g / L, the stirring speed to 200 rpm, the concentration of the surfactant to be maintained at 0.02 mol / L, and performing a coprecipitation reaction to obtain a primary mixed solution containing a first precipitate with a D50 particle size of 5 μm;

[0120] The second stage: adding the mixed metal salt solution, sodium hydroxide solution and ammonia water to the obtained primary mixed solution in parallel, and continuously adding the surfactant, the adding rate of the mixed metal salt solution is 35 L / h, the pH is adjusted to 10.3-10.5, the ammonia concentration is 3.5 g / L, the stirring speed is 180 rpm, the concentration of the surfactant is maintained at 0.02 mol / L, and a coprecipitation reaction is carried out to obtain a remixed solution containing a second precipitate with a D50 particle size of 7 μm;

[0121] The third stage: adding the mixed metal salt solution, sodium hydroxide solution and ammonia water to the obtained remixed liquid in parallel, and continuously adding the surfactant, the addition rate of the mixed metal salt solution is 45L / h, the pH is adjusted to 10.0-10.2, the ammonia concentration is 3g / L, the stirring speed is 150rpm, the concentration of the surfactant is maintained at 0.02mol / L, and a coprecipitation reaction is carried out to obtain a final mixed liquid containing a precursor with a D50 particle size of 9μm.

[0122] This embodiment also provides a boron-coated positive electrode material, in which the mass fraction of boron element in the positive electrode material is 0.02wt%, and the preparation process of the boron-coated positive electrode material is as follows:

[0123] The precursor having a mass ratio of 1:1.2 is mixed with a lithium source, and the mixture is sintered at 800°C for 6 hours to obtain a sintered product; the sintered product is mixed with boric acid, and the mixture is sintered at 200°C for 6 hours to obtain a boron-coated positive electrode material.

[0124] Example 3

[0125] This embodiment provides a precursor that is loosened in radial direction, the precursor comprising a seed crystal, and a shell layer coated outside the seed crystal with a density lower than that of the seed crystal;

[0126] In the radial direction of the precursor, along the direction from close to the seed crystal to far away from the seed crystal, the shell layer includes a first shell layer, a second shell layer and a third shell layer which are sequentially covered and have successively smaller densities.

[0127] The preparation method of the precursor is:

[0128] (1) adding a mixed metal salt solution (the total concentration of metal ions is 2.5 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 96:2:2), potassium hydroxide solution and ammonia water to the reaction bottom liquid in parallel, adjusting the pH to 11.2-11.5, the ammonia concentration to 6 g / L, the stirring speed to 400 rpm, and the temperature to 40° C., to carry out a coprecipitation reaction, and sequentially carry out solid-liquid separation, washing and drying to obtain a seed crystal with a D50 particle size of 5 μm and a first slurry, and then adding the obtained seed crystal, water and ammonia water to the first slurry in parallel to obtain a second slurry with a seed crystal solid content of 60 g / L, an ammonia concentration of 6 g / L and a temperature of 50° C.;

[0129] The addition rate of the mixed metal salt solution was 10 L / h, the pH of the reaction bottom solution was 12, the ammonia concentration was 10 g / L, and the temperature was 40°C;

[0130] (2) adding a mixed metal salt solution (the total concentration of metal ions is 2.5 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 96:2:2), potassium hydroxide solution and ammonia water in three stages to the second slurry obtained in step (2), adjusting the reaction conditions, and performing a coprecipitation reaction to obtain the precursor;

[0131] The first stage: adding a mixed metal salt solution, a potassium hydroxide solution and an ammonia solution to the second slurry obtained in step (1) in parallel, and continuously adding a surfactant, the adding speed of the mixed metal salt solution is the same as the adding speed of the mixed metal salt solution in step (1), adjusting the pH to 10.8-11.0, the ammonia concentration to 5 g / L, the stirring speed to 350 rpm, the concentration of the surfactant to be maintained at 0.1 mol / L, and performing a coprecipitation reaction to obtain a primary mixed solution containing a first precipitate with a D50 particle size of 7 μm;

[0132] The second stage: adding the mixed metal salt solution, potassium hydroxide solution and ammonia water to the obtained primary mixed solution in parallel, and continuously adding the surfactant, the adding rate of the mixed metal salt solution is 25 L / h, the pH is adjusted to 10.5-10.8, the ammonia concentration is 4.5 g / L, the stirring speed is 300 rpm, the concentration of the surfactant is maintained at 0.1 mol / L, and a coprecipitation reaction is carried out to obtain a remixed solution containing a second precipitate with a D50 particle size of 9 μm;

[0133] The third stage: adding the mixed metal salt solution, potassium hydroxide solution and ammonia water to the obtained remixed liquid in parallel, and continuously adding the surfactant, the addition rate of the mixed metal salt solution is 35L / h, the pH is adjusted to 10.3-10.5, the ammonia concentration is 4g / L, the stirring speed is 250rpm, the concentration of the surfactant is maintained at 0.1mol / L, and a coprecipitation reaction is carried out to obtain a final mixed solution containing a precursor with a D50 particle size of 15μm.

[0134] This embodiment also provides a boron-coated positive electrode material, in which the mass fraction of boron element in the positive electrode material is 0.005wt%, and the preparation process of the boron-coated positive electrode material is as follows:

[0135] The precursor having a mass ratio of 1:1 is mixed with a lithium source, and the mixture is sintered at 500° C. for 10 hours to obtain a sintered product; the sintered product is mixed with boric acid, and the mixture is sintered at 500° C. for 2 hours to obtain a boron-coated positive electrode material.

[0136] Example 4

[0137] This embodiment provides a precursor that is loosened in radial order. Except that the D50 particle size of the seed crystal obtained in step (1) of the preparation method of the precursor is 4 μm, the rest is the same as that of Embodiment 1.

[0138] This embodiment also provides a boron-coated positive electrode material. The preparation process of the positive electrode material is the same as that of Example 1 except that the precursor in the present application is used for preparation.

[0139] Example 5

[0140] This embodiment provides a precursor that is loosened in radial order. Except that in step (2) of the method for preparing the precursor, the concentration of the surfactant in the first stage, the second stage and the third stage is adjusted to 0.06 mol / L, the rest is the same as that in Example 1.

[0141] This embodiment also provides a boron-coated positive electrode material. The preparation process of the positive electrode material is the same as that of Example 1 except that the precursor in the present application is used for preparation.

[0142] Example 6

[0143] This embodiment provides a precursor which is loosened in radial order similar to that in Embodiment 1.

[0144] This embodiment further provides a boron-coated positive electrode material, which is the same as that of Embodiment 1 except that the mass fraction of boron element in the positive electrode material is 0.02 wt %.

[0145] Example 7

[0146] This embodiment provides a precursor that is loosened in radial order. Except that the D50 particle size of the seed crystal obtained in step (1) of the preparation method of the precursor is 1 μm, the rest is the same as that of Embodiment 1.

[0147] This embodiment also provides a boron-coated positive electrode material. The preparation process of the positive electrode material is the same as that of Example 1 except that the precursor in the present application is used for preparation.

[0148] Example 8

[0149] This embodiment provides a precursor that is loosened in radial order. Except that the D50 particle size of the seed crystal obtained in step (1) of the precursor preparation method is 5.5 μm, the rest is the same as that of Example 1.

[0150] This embodiment also provides a boron-coated positive electrode material. The preparation process of the positive electrode material is the same as that of Example 1 except that the precursor in the present application is used for preparation.

[0151] Example 9

[0152] This embodiment provides a precursor that is loosened in radial order. Except that in step (2) of the method for preparing the precursor, the concentration of the surfactant in the first stage, the second stage and the third stage is adjusted to 0.01 mol / L, the rest is the same as Example 1.

[0153] This embodiment also provides a boron-coated positive electrode material. The preparation process of the positive electrode material is the same as that of Example 1 except that the precursor in the present application is used for preparation.

[0154] Example 10

[0155] This embodiment provides a precursor that is loosened in radial order. Except that in step (2) of the method for preparing the precursor, the concentration of the surfactant in the first stage, the second stage and the third stage is adjusted to 0.2 mol / L, the rest is the same as Example 1.

[0156] This embodiment also provides a boron-coated positive electrode material. The preparation process of the positive electrode material is the same as that of Example 1 except that the precursor in the present application is used for preparation.

[0157] Embodiment 11

[0158] This embodiment provides a precursor which is loosened in radial order similar to that in Embodiment 1.

[0159] This embodiment further provides a boron-coated positive electrode material, which is the same as that of Embodiment 1 except that the mass fraction of boron element in the positive electrode material is 0.002 wt %.

[0160] Example 12

[0161] This embodiment provides a precursor which is loosened in radial order similar to that in Embodiment 1.

[0162] This embodiment further provides a boron-coated positive electrode material, which is the same as that of Embodiment 1 except that the mass fraction of boron element in the positive electrode material is 0.03 wt %.

[0163] Comparative Example 1

[0164] This comparative example provides a precursor, wherein the first shell layer, the second shell layer and the third shell layer have the same density in the radial direction of the precursor, from the direction close to the seed crystal to the direction away from the seed crystal. That is, in the preparation method of the precursor, in the second stage and the third stage of step (2), the addition rate of the metal salt solution, the pH adjusted during coprecipitation, the ammonia concentration, the stirring speed and the concentration of the surfactant are the same as those in Example 1, and the rest are the same as those in Example 1.

[0165] Comparative Example 2

[0166] This comparative example provides a precursor which is loosened in radial order as in Example 1.

[0167] This embodiment also provides a positive electrode material, which does not contain boron element. That is, except for the step of sintering the obtained sintered product mixed with boric acid in the preparation method of the positive electrode material, the rest is the same as that of Example 1.

[0168] The positive electrode materials provided in the above embodiments and comparative examples are used to prepare a lithium-ion battery: the obtained positive electrode material, conductive carbon black SP (TIMCAL) and polyvinylidene fluoride PVDF (HSV900) are mixed in a mass ratio of 90:5:5, N-methylpyrrolidone is used as a 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 um; after coating, it is first blown and dried, 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;

[0169] The charge and discharge test was carried out at a voltage window of 2.8-4.3V with 0.1C / 0.1C charge and discharge to obtain the initial discharge capacity. The 0.1C rate performance and the capacity retention rate after 100 cycles are shown in Table 1.

[0170] Table 1

[0171]

[0172]

[0173] From Table 1, we can get:

[0174] (1) The lithium-ion battery prepared using the positive electrode material prepared in Examples 1 to 6 of the present invention exhibits a high initial discharge capacity, excellent rate performance and strong cycle stability;

[0175] (2) By comparing Example 1 with Examples 7 and 8, it can be seen that the D50 particle size of the seed crystal obtained in the preparation method of the precursor in the present invention will affect the performance of the lithium-ion battery; when the D50 particle size of the seed crystal is too small or too large, the battery capacity will be reduced, and the rate performance and cycle performance will decrease; this is because a smaller D50 particle size of the seed crystal will expand the particle size range of the porous structure layer, increase the porosity of the material, and thus increase the contact area between the material and the electrolyte, which is not conducive to improving the rate performance and cycle performance of the material; a larger D50 particle size of the seed crystal will reduce the particle size range of the porous structure layer, reduce the porosity of the material, and increase the internal resistance of the material, thereby causing the rate performance to deteriorate;

[0176] (3) By comparing Example 1 with Examples 9 and 10, it can be seen that the concentration of the surfactant in the first stage, the second stage and the third stage of step (2) in the preparation method of the precursor of the present invention will affect the performance of the lithium-ion battery. In the present invention, by adding a surfactant in the first stage, the second stage and the third stage, the surfactant can prevent the primary particles formed during coprecipitation from sticking together, and can make the primary particles grow in the direction of slender strips, thereby increasing the pores between the primary particles, which is conducive to forming a loose and porous structure, thereby shortening the transmission path of lithium ions in the positive electrode material prepared from the precursor and reducing the internal resistance; when the concentration of the surfactant is too small or too large, it will lead to a lower battery capacity, and the rate performance and cycle performance will decrease; this is because, when the concentration of the surfactant is low, the loose and porous structure cannot be well formed inside the material, which is not conducive to the transmission of lithium ions; when the concentration of the surfactant is high, it will affect the orderly arrangement of the primary particles, thereby reducing the electrochemical performance of the material;

[0177] (4) By comparing Example 1 with Examples 11 and 12, it can be seen that the mass fraction of the boron element in the boron-coated positive electrode material of the present invention will affect the performance of the lithium-ion battery; when the mass fraction of the boron element is too high or too low, the battery capacity will be reduced, and the rate performance and cycle performance will decrease; this is because, when the mass fraction of the boron element is low, the uniform coating of the material surface cannot be achieved, and side reactions will occur when the material contacts the electrolyte, thereby affecting the battery performance; when the mass fraction of the boron element is high, the coating layer on the material surface will be thicker, which will increase the mass transfer impedance and be unfavorable for the transmission of lithium ions, thereby reducing the rate performance and cycle performance.;

[0178] (5) By comparing Example 1 with Comparative Example 1, it can be seen that the precursor provided by the present invention has a higher seed density and a lower shell density, thereby forming a structure that is compact inside and looser from the inside to the outside, thereby reducing the internal resistance of the positive electrode material prepared from the precursor and shortening the lithium ion transmission path of the positive electrode material; therefore, the battery containing the positive electrode material prepared from the precursor exhibits excellent electrochemical performance;

[0179] (6) By comparing Example 1 with Comparative Example 2, it can be seen that the positive electrode material in the present invention has a boron coating layer, which avoids the corrosion of the electrolyte on the positive electrode material, thereby improving the rate performance and stability of the battery containing the positive electrode material.

[0180] The above description is only a specific implementation mode 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 are within the protection scope and disclosure scope of the present invention.

Claims

1. A precursor that is loosened in radial order, characterized in that: The precursor includes a seed crystal and a shell layer covering the seed crystal; The density of the shell layer is lower than the density of the seed crystal, and in the radial direction of the precursor, the density of the shell layer decreases in sequence from the direction close to the seed crystal to the direction away from the seed crystal.

2. The precursor according to claim 1, characterized in that Along the direction from close to the seed crystal to far away from the seed crystal, the shell layer includes a first shell layer, a second shell layer and a third shell layer which are sequentially covered and have successively decreasing densities.

3. A method for preparing the precursor according to claim 1 or 2, characterized in that: The preparation method comprises: (1) adding a mixed metal salt solution, a precipitant solution and a complexing agent solution to a reaction base solution in parallel, adjusting the reaction conditions, and performing a coprecipitation reaction to obtain seed crystals and a first slurry, and then adding the obtained seed crystals to the first slurry to obtain a second slurry; (2) adding the mixed metal salt solution, the precipitant solution and the complexing agent solution to the second slurry obtained in step (1) in stages and in parallel, adjusting the reaction conditions, and performing a coprecipitation reaction to obtain the precursor; The staged addition comprises at least two stages, wherein the addition rate of the mixed metal salt solution in the first stage of the staged addition is not lower than the addition rate of the mixed metal salt solution in step (1), and the addition rate of the mixed metal salt solution in each previous stage is lower than the addition rate of the mixed metal salt solution in the adjacent next stage.

4. The preparation method according to claim 3, characterized in that: The addition rate of the mixed metal salt solution in step (1) is 10 to 80 L / h; Preferably, the pH of the reaction liquid in step (1) is 11-12, the ammonia concentration is 4-10 g / L, and the temperature is 40-80° C.; Preferably, the adjusting reaction conditions in step (1) include adjusting the pH to 11-11.5, the ammonia concentration to 5-6 g / L, and the stirring speed to 200-400 rpm; Preferably, the adjusting the reaction conditions in step (1) comprises adjusting the temperature to 40-60°C; Preferably, the D50 particle size of the seed crystal in step (1) is 2 to 5 μm; Preferably, when the seed crystals obtained in step (1) are added to the first slurry, water and a complexing agent solution are added simultaneously; Preferably, the solid content of the seed crystals in the second slurry obtained in step (1) is 20-60 g / L, the ammonia concentration is 4-6 g / L, and the temperature is 50-70°C.

5. The preparation method according to claim 3 or 4, characterized in that: The step (2) comprises three stages, wherein the adding speed of the mixed metal salt solution increases successively, the pH value decreases successively, the ammonia concentration decreases successively, and the stirring speed decreases successively in the first stage, the second stage, and the third stage; Preferably, in the first stage, the mixed metal salt solution, the precipitant solution and the complexing agent solution are added in parallel to the second slurry obtained in step (1), the reaction conditions are adjusted, and a co-precipitation reaction is performed to obtain a primary mixed solution containing a first precipitate; Preferably, the rate of addition of the mixed metal salt solution in the first stage is the same as the rate of addition of the mixed metal salt solution in step (1); Preferably, the adjusting reaction conditions in the first stage include adjusting the pH to 10.5-11.0, the ammonia concentration to 4-5 g / L, and the stirring speed to 200-350 rpm; Preferably, the first stage further comprises continuously adding a surfactant to the second slurry; Preferably, the concentration of the surfactant during the coprecipitation reaction in the first stage is maintained at 0.02-0.1 mol / L; Preferably, the D50 particle size of the first precipitate obtained in the first stage is 5 to 7 μm; Preferably, in the second stage, the mixed metal salt solution, the precipitant solution and the complexing agent solution are added to the obtained primary mixed solution in parallel, the reaction conditions are adjusted, and a co-precipitation reaction is performed to obtain a remixed solution containing a second precipitate; Preferably, the addition rate of the mixed metal salt solution in the second stage is 25 to 35 L / h; Preferably, the adjusting reaction conditions in the second stage include adjusting the pH to 10.3-10.8, the ammonia concentration to 3.5-4.5 g / L, and the stirring speed to 180-300 rpm; Preferably, the second stage further comprises continuously adding a surfactant to the initial mixed liquid; Preferably, the concentration of the surfactant during the coprecipitation reaction in the second stage is maintained at 0.02-0.1 mol / L; Preferably, the D50 particle size of the second precipitate obtained in the second stage is 7 to 9 μm; Preferably, in the third stage, the mixed metal salt solution, the precipitant solution and the complexing agent solution are added to the obtained remixed solution in parallel, the reaction conditions are adjusted, and a coprecipitation reaction is performed to obtain a final mixed solution containing the precursor; Preferably, the addition rate of the mixed metal salt solution in the third stage is 35 to 45 L / h; Preferably, the adjusting reaction conditions in the third stage include adjusting the pH to 10.0-10.5, the ammonia concentration to 3-4 g / L, and the stirring speed to 150-250 rpm; Preferably, the third stage further comprises continuously adding a surfactant to the initial mixed liquid; Preferably, the concentration of the surfactant during the coprecipitation reaction in the third stage is maintained at 0.02-0.1 mol / L; Preferably, the D50 particle size of the precursor obtained in the third stage is 9 to 15 μm.

6. A boron-coated positive electrode material, characterized in that: The positive electrode material is prepared from the precursor according to claim 1 or 2.

7. The positive electrode material according to claim 6, characterized in that The mass fraction of the boron element in the positive electrode material is 0.005-0.02 wt %.

8. A process for preparing the positive electrode material according to claim 6 or 7, characterized in that: The preparation process comprises: The precursor is mixed with a lithium source and then sintered once to obtain a sintered product. The sintered product is mixed with a boron source and then sintered twice to obtain a boron-coated positive electrode material.

9. The preparation process according to claim 8, characterized in that: The mass ratio of the precursor to the lithium source is 1:(1-1.2); Preferably, the primary sintering temperature is 500-800°C and the time is 6-10h; Preferably, the secondary sintering is carried out at a temperature of 200 to 500° C. and for a time of 2 to 6 hours.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material according to claim 6 or 7.

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